Weekly Field Update – 5/3/21

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Coastal

Rob Last reports, “Botrytis (gray mold) is evident in places following rainfall. Sanitation and removal of the infected berries are critical to reducing inoculum loading. Fungicide applications will also be required to prevent spore germination and further spread of the disease. Where spider mite treatments have been applied, they have effectively reduced the populations but will still require scouting and monitoring.  Yields achieved are very good. Cucurbit crops continue to develop well with a low incidence of chill injury from the cooler temperatures observed on April 21/22. Crops are running well, with some flowering being observed. Cucumber beetles are being monitored, and a few aphids are present in places. Cucumber beetles observed are currently below the threshold of 5 beetles per plant. Squash bugs are also being found on some sites. Careful monitoring will be required because numbers can increase rapidly. Crops are free from disease; however, protectant fungicides are still a critical input. Blueberries are swelling well and beginning to blush.  Blackberries are flowering with excellent fruit set and bud formation. Spider mites have been evident in these crops too; however miticide applications are proving very effective.

Squash bugs are showing up in the coastal region. Photo from Rob Last.

Zack Snipes reports, “We had another nice week of weather in the Lowcountry. We are starting to dry out again so some rain would be nice. All of our crops look really great right now with no huge issues. The biggest issue I see right now is spider mites on all crops which makes sense with the warm dry weather. I’ve gotten a few calls about some strawberry plants putting out runners. We need to get in the fields and pinch those off while we are cleaning up dead berries, blossoms, and tissue. I have been in several vegetable fields lately and seen some inconsistencies in plant growth and vigor. Upon further inspection of some tomato and squash crops, I found galling on the roots which is an indicator of root-knot nematodes. If this is the case on your farm, pull up a few plants and look at the roots. We need to keep good notes on where these areas or fields are and practice good crop rotation for next season or use resistant cultivars. There are some cover crops that help with suppression as well. If you want to pull a soil sample to check for nematodes, give your local agent a call. We are doing a statewide survey looking for the guava root-knot nematode and can assist with sampling. In case you missed the “Update from the Tomato Fields” talk last Wednesday, here is the link.

Smaller squash plants in a large field made me question root-knot nematode damage.  Upon inspection of the roots, I found galling which is an indicator of nematode pressure. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “The weather last week was mild and it is very dry again. The inch of rain we got last weekend didn’t go very far. Strawberries are still yielding well, though in some fields, we’re starting to see berry size decrease, like we frequently see towards the end of picking. Folks had to remove water-damaged berries from their fields following the rain this past weekend. I guess the silver lining in this dry spell is we haven’t had many water-damaged berries yet this year. We’re still seeing some mites here and there, but disease pressure remains low. I found a berry last week with an anthracnose fruit rot lesion for the first time this season. So even though disease pressure is low, we still need to keep up with fungicide programs. There is some rain in the forecast for this week, so now would be a good time to throw in one of the site specific fungicides.”

Fungicides with the best efficacy on gray mold (left) and anthracnose (right) Photo from MyIPM app.
Cabbage with some cold damage from the cold a little over a week ago. Photo from Justin Ballew

Sarah Scott reports, “Along the Ridge, crews are still finishing up thinning in peach orchards to ensure good sizing on fruit. We are well into our summer cover spray programs for the season. During pit hardening it is critical to do preventative treatment for bacterial spot. Growers should be watching for plum circulio activity as well as scale crawlers in the next week as well. Sime powdery mildew has been found on foliage. Refer the the 2021 SE Peach, Nectarine, and Plum Management Guide for specific treatment recommendations. Strawberries are performing well. Some spider mite activity as well as some botrytis in the fields, which could worsen with several days of wet weather in the forecast. Transplanting of summer crops continues, including tomatoes and peppers. Curcurbits are becoming established and harvest will begin soon. 

Peach tree after thinning. Notice all of the green fruit on the ground surrounding it. Photo from Sarah Scott.

Pee Dee

Tony Melton reports, “Tomatoes, peppers, cucumber, and sweet potato slips are really growing since it has warmed up. Getting ready to sidedress and plow cucumbers. Fresh market cabbage will be ready to harvest soon. Processing collards are almost ready to harvest- some downy mildew has been seen. Asparagus suffered from excessive rains last year. Saw some sunscald and chemical burn on strawberries, so watch what products you are applying foliar, especially fertilizers. With the small amount of rain we had last week many acres of peas have been planted; however, it is awfully dry again.”

Weekly Field Update – 4/26/21

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Join us this Wednesday (3/24/21) at 12:30 pm for an update from the tomato fields with Zack Snipes. It will be a relatively short meeting, lasting 30-45 minutes, so tune in while you eat your lunch. Click here to register.

Coastal

Rob Last reports, “Crops in the area continue to develop well, and I expect this to continue after some welcome rainfall over the weekend.  Following the rain over the weekend and returning to warm temperatures, keep scouting for diseases in crops and ensure fungicide applications are made promptly. Spider mites show activity in a range of crops from strawberries to peppers, tomatoes, and blackberries. Always remember to use a specific miticide for spider mite control to avoid flaring populations. Cucumber beetles are beginning to be found in sticky traps. Currently, no damage is being seen to crops. Treatment options include neonicotinoid insecticides applied as a foliar spray or through the drip system.  When treatments are made, it is possible feeding damage will be seen as the pests need to ingest the pesticide.”

Zack Snipes reports, “We finally got some rain last week that I think will benefit all of our crops. Spider mites were the talk of the community last week. I saw high populations on strawberries as well as blackberries. On farms with mixed produce, you will want to scout all crops, even if they are at a stage where they normally wouldn’t have mites. I found mites on tomatoes last week because they were adjacent to a strawberry crop. We need to get on top of this pest before its too late. There are plenty of IPM techniques and strategies for this pest. Also, if you have sprayed a product in strawberry and are considering treating other crops nearby, you may want to rotate products/chemistries from what you sprayed on strawberry. Chances are those are the same genetically similar spider mites so if you had any resistance in strawberry, or another crop, then you may see it on tomato or watermelon.”

Taking good photos of spider mites is tough but on this leaf you can see several two-spotted spider mites. Don’t wait until you see symptomatic damage to manage this pest.    

Midlands

Justin Ballew reports, “We had a cold event in the midlands that seems like it got around 5 degrees colder in most areas than what the forecast called for. It got to 35 at my house Wednesday night/Thursday morning. South of Columbia and Lake Murray, I only heard a couple reports of light frost, but north of Columbia, I heard reports of the temperatures reaching 31. We’re certainly going to see some damage in those areas to spring crops that weren’t covered. On another note, strawberries are yielding really well right now. Growers are reporting that yields are at times outpacing sales. We finally got some rain this weekend (just under an inch at my house), so we’re going to see some water-damaged berries and the moisture will give grey mold an opportunity to increase. The rain was good news for spider mite management, as their populations had been thriving in the dry conditions. Diamondback moth populations are increasing in brassicas, so keep up with scouting.”

Strawberries have been yielding well and berry size has been quite large on some cultivars. Photo from Justin Ballew
We haven’t seen much grey mold lately, but the rain we had over the weekend may allow it to make a comeback. Photo from Justin Ballew

Pee Dee

Bruce McLean reports, “Last week’s brief kiss of frost doesn’t appear to have caused any significant problems on the crops. But, it is starting to get a bit dry. Sweet corn and pea emergence has been looking good, with most locations having an excellent stand. Cucurbit crops are starting to emerge, as well. Transplant tomatoes are looking very good. Everyone is taking advantage of this beautiful weather to plant vegetable crops and blueberries… just don’t forget to irrigate. Strawberry harvest is peaking right now and the fruit looks really good. Disease pressure is pretty low, but spider mite activity is high in many locations. In blueberries, much of the damaged fruit (from the Easter freeze) is beginning to shed off of the plant. Hopefully, this will continue… so lingering damaged fruit will not slow down harvest (starting in a few weeks). Muscadines are starting to show some early flower bud development.”

Early flower bud development in Carlos muscadine. Photo from Bruce McLean.
Crimson clover cover crop in a muscadine vineyard is a beautiful sight to see. It serves as a great habitat for beneficial insects. Photo from Bruce McLean.
Blueberries planted on plastic mulch covered beds. The plastic reduces the development of weeds, thereby reducing competition for the newly planted blueberry plants. Photo from Bruce McLean.

Tony Melton reports, “Peppers, cucumber, and tomatoes are just sitting and not growing. Extra fertilizer will do little for growth in these cool conditions. Cabbage needs to be sprayed for thrips, sclerotinia, and caterpillars. Cabbage, collards, and greens are loving the cool weather and hauling butt, so side-dress to keep growing. Strawberries are loving these cool conditions and are really producing. We are having an overabundance of local strawberries making them hard to sell – many are being discarded. Just a small amount of wind damage. Tomatoes, peppers, and cucumber plants were not big enough to act like a sail and be blown (twisted-off) in the wind. Got just enough rain to start planting dryland peas. I know I will regret saying this – “but I hope it warms up soon.”

Upstate

Kerrie Roach reports, “Every day brings us a little closer to May in the Upstate, and with that brings a little less chance of a frost or freeze event. Last week Thursday brought on lows of 30-32 degrees F in many places causing damage to warm season crops as well as landscapes across the upstate. Strawberry growers have slowed since the cool weather, but production will start to pick back up with warmer days and nights this week.”

Coronavirus Food Assistance Program 2 Reopened

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From Clemson Agribusiness Agent Kevin Burkett.

Beginning April 5th, USDA Farm Service Agency began accepting new and modified CFAP 2 applications. Agriculture Secretary Tom Vilsack announced on March 24 the U.S. Department of Agriculture will begin providing additional financial assistance to farmers, ranchers, and producers impacted by COVID-19 market disruptions. This is part of a larger effort to reach a greater share of farming operations and improve USDA pandemic assistance.  

USDA reopened CFAP 2 signup for all eligible producers beginning April 5, 2021. The CFAP 2 signup period has reopened as part of USDA’s new Pandemic Assistance for Producers initiative. The original application period for CFAP 2 was September 21 through December 11, 2020. A deadline for signup for the reopened CFAP 2 has not been announced. Many common South Carolina fruits, vegetables, tree nuts and herb crops are eligible.

Note: Participation in CFAP 1 is NOT required for assistance through CFAP 2.

More information for specialty crop producers.

Apply for CFAP 2.

Weekly Field Update – 4/19/21

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Coastal

Zack Snipes reports, “We had some nice weather last week. The tomato crop is looking great as are most of our cucurbits and greens. I am seeing increased caterpillar pressure across the area. We had several calls from across the state early last week about sunburned strawberries. We went and visited the farms and tried to rule out disease, frost damage, etc. The only thing we came up with is some sort of sunburn damage. This was most prevalent on the southern facing sides of beds where there was poor canopy coverage. I also saw damaged tissue on tender lettuce, in my citrus plots at the CREC, and on some new shoots of ornamentals at my house. I checked the solar radiation at the weather station at the CREC and the units (W/m2) were 300-500 units higher on Monday when compared to the prior 4 days. Perhaps we had intense UV levels and higher temperatures that led to this damage? Here is a really great article on the types of sunburn on plants and fruit.”

Discolored, damaged, and unmarketable strawberries. Photo from Zack Snipes.
The berries were clean on the inside and had no bad odors or flavor. Photo from Zack Snipes.
Solar radiation measurement from a weather station at Coastal REC in Charleston. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “The weather was a little cooler last week and we are really dry here in the midlands. I’ve had less than 4 tenths of an inch of rain so far in the month of April. This has been really helpful for disease management in strawberries. I’ve seen very little grey mold compared to years past. Spider mites are enjoying the dry weather, though. I’m starting to see populations really grow, so keep a close eye on that. Caterpillar populations appear to be building, though overall they are still low on spring planted brassicas. Tomatoes and cucurbits have been going in the ground and doing well so far. Sweet corn is growing well and it’s hard to even tell some of the leaves were burned by the cold a couple weeks ago.”

Two-spotted spider mites on the underside of a strawberry leaf. Photo from Justin Ballew.
If a treatment is needed for mites, use a dedicated miticide. Using broad spectrum insecticides kills beneficials, like this lacewing, which can lead to explosive mite population growth. Photo from Justin Ballew.

Sarah Scott reports, “Peach producers are continuing thinning fruit since we feel that we have a good assessment of what was damaged by cold. Growers who have varieties with significant losses may want to take a look at a reduced spray schedule to ensure adequate disease and pesticide coverage for the season. It’s important to maintain orchards even if they are not going to produce a crop to maintain the health of the trees.”

Pee Dee

Tony Melton reports, “Cool night temperatures making strawberries, cabbage, collards, and greens happy. We are actually having a true spring this year. Labor is our #1 problem for small growers. Some crops have been destroyed by mistakenly applying the wrong chemicals, especially atrazine since corn is being planted now. Hundreds of acres of tomatoes, peppers, and cucumbers are already planted and holding their own.”

Upstate

Kerrie Roach reports, “Peach and apple damage continues to be assessed. Weather forecasts in northern Oconee County for Tuesday night/Wednesday morning predict more cold weather, but growers are hoping for temperatures to stay above freezing as forecasted. Strawberries in the Upstate are starting to ripen. Last week most fields were being spot picked, but with warm sunny days many of the u-pick operations are beginning to open this week. The cold temperatures predicted Tuesday night/Wednesday morning could become an issue for berry growers depending on location, elevation, and air movement.”

Weekly Field Update – 4/12/21

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Statewide

Dr. Matt Cutulle reports, “I am starting to see some goosegrass popping due to soil temperatures being 65 F. Goosegrass will typically be problematic in more compacted areas of the field. In most broadleaf crops a Select or Poast post-emergent application will control emerged goosegrass. PRE herbicide options include Curbit and Dual Magnum (If crop is labeled). In rice it is important to remember that Quinclorac products will kill crabgrass but not goosegrass. The best rice product that will control goosegrass effectively in SC is Clincher.”

Coastal

Rob Last reports, “Crops are generally doing well in the area, with strawberries coming off with good volumes. On the whole, row covers or icing protected 97% of the susceptible flowers leading to 1-2% losses of flowers. The damaged flowers can increase grey mold pressure in the crops so, maintaining both sanitation and fungicide applications to strawberries will be crucial. As berries ripen, sanitation also becomes essential for reducing pest pressure from sap beetles. In some crops, where row covers were utilized, we see spider mite populations increasing and a few active thrips feeding on both flowers and berries. Other fruit crops in the area, such as blackberries and blueberries, look very good with low levels of damage from the freeze event last weekend. Peaches in the area are being thinned, with scouting being maintained for scale and plum curculio. Early planted watermelons did suffer from the frost in places, leading to 10-15% plant loss and hence the need to replant in a few areas. Other crops are moving slowly away from the injuries. Luckily a lot of crops were not beginning to vine and survived the worst of the damage. These plants are stressed, so care will be needed with any applications as well as scouting for pest and disease issues. Conversely, Cantaloupes in the area were direct seeded and have survived unscathed.”

Zack Snipes reports, “I was out and about last week as things are moving rather quickly in the fields. Spider mites are alive and active in every strawberry patch that I was in last week. You will see the translucent mite with 2 distinct spots as well as a reddish colored mite. The reddish colored mite is actually a two-spotted spider mite. We see this red form early in the season. Get out and scout as the weather is perfect for them. I am also seeing strawberry plants wilting down and dying. If you cut the crown you will see a brown/red rot in the center of the crown. Send these plants off for diagnosis. Most of what I have seen has been Phytophthora. We lost some cucurbit crops to the frost last weekend but some areas had no damage at all or slight damage. For some positive news, we are cutting some beautiful broccoli right now.”

Lower lying areas of fields or areas where the drip tape was nicked is where I am seeing some root rot issues. Photo from Zack Snipes.
Cutting the crown of wilting strawberry plants can help detect the pathogen responsible.  Sending off to the lab is the only way to get a 100% diagnosis of the problem. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “Strawberry picking started on a wider scale this past week. This conveniently coincided with spring break for a lot of the public schools in our area, so U-pick operations have been busy. The weather was very mild last week, so everything is looking great. Spider mite and grey mold activity seems to be very low. There are a few thrips in certain places, so that’s something we need to keep an eye on. Brassicas are growing well. Caterpillar populations are still pretty low in most spring planted crops. There was a little injury to sweet corn from the recent frosts, but we expect the plants to grow out of it. Sweet corn’s growing point is underground until the 6 leaf stage. Since pretty much all the sweet corn was at the 3 leaf stage or younger, the growing points were protected and the damage is just superficial.”

Strawberry season has finally arrived in the Midlands. Photo from Justin Ballew.

Sarah Scott reports, “We are still assessing peach crop damage from freeze events happening between 4/1 and 4/3. It looks like anywhere from 1/4 to 1/3 of fruitlets were damaged by the cold event but with no additional damage we should still be on track for a good crop this year.  Strawberries were delayed a bit from the cold but are recovering nicely. Planting continues for crops like kale and other spring greens.”

Peach fruitlets at shuck off. Photo from Sarah Scott.

Pee Dee

Bruce McLean reports, “Strawberries are really starting to come off. The quality is very good, and the plants are in good health. Disease is relatively low and spider mite activity is moderate. Damage was minimal from the freeze before Easter. We did see some damage on blueberries, though. Blueberries without frost protection (in especially cold locations) did see some significant injury to both early southern highbush and early rabbiteye cultivars. Injury of 80% was observed in Star and O’Neal (southern highbush) and Premier (rabbiteye). Blueberries with frost protection fared much better. This shows the importance of having well-designed frost protection if you are going to grow early-blooming cultivars. Muscadines, being at budbreak, did not show any significant injury. Farmers are taking advantage of this absolutely beautiful weather to plant vegetables. Sweet corn, peas, butterbeans, cucumbers, squash, melons, tomatoes, etc. are going in the ground as fast as they can. Blueberries are being planted now too.

Black and brown seed and tissue within the berry shows that the fruit was injured from the freeze and will not develop. Photo from Bruce McLean.
Damage to early fruitlets on rabbiteye blueberry. Photo from Bruce McLean.

Tony Melton reports, “Most strawberries are doing well and really starting to produce a lot of fruit. Cabbage is starting to head and is growing well. Brassica growers are applying products for diamondback moth and Sclerotinia. Some pickles are emerging and many acres will be planted this week. Some butterbeans are up and more are being planted. We will start to planting peas this week. Cool temperatures slowed sweetpotato slip growth a little, but most beds are covered with slips. Collards, turnips, and kale are growing fast. Hundreds of acres of tomatoes and peppers are already planted. A few acres of watermelons and cantaloupes are planted, but our main market is after the 4th of July.”

Weekly Field Update – 4/5/21

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Coastal

Zack Snipes reports, “Temperatures checked in at 28 F at the northern end of Charleston County one night this past week. Strawberries were covered but some blossoms are showing damage. The weather this week should really push berries and give us our first big flush of the season. Lots of acres of tomatoes are planted and before the cold were looking pretty good.  Time will tell how much the cold will slow them down. It has been very windy in the Lowcountry as well which I think has slowed down development on some crops. Spring brassicas are looking great with very low worm pressure right now. That does not mean we should stop scouting. Populations can jump very quickly.”

Tomatoes were looking ok before the cold nights. Photo from Zack Snipes.
A fall seeded brassica crop beside strawberries is blooming. The thought behind this cover crop is the early blooms will encourage beneficial insects that will prey on the early season thrips which have been causing lots of cosmetic damage on strawberries the past few years. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “We had a couple frosts late last week and the temperature got down to 30 degrees at my house. Growers covered their strawberry fields, so we don’t expect to see any damage there. We’re getting very close to picking on a larger scale. I’ve seen some nutrient deficiencies in a few strawberry fields, so be sure to tissue sample periodically and adjust fertigation accordingly. Now that we’re into April and the forecast looks warm, many growers will begin planting cucurbit crops this week. A few already had seed in the ground before the frost. The first plantings of sweet corn are up and growing well.”

One of the first plantings of sweet corn is up and looking good. Photo from Justin Ballew.

Pee Dee

Tony Melton reports, “Still determining damage from frost. One grower had 40 A of butterbeans emerging – sprayed with a frost control product. Sweet potatoes slips are up, covered with plastic, and beds are covered with slips (about a month out from planting). Cabbage is beginning to cup, head, and touch in the rows. Asparagus was hurt by cold and most harvest is over. Starting to plant pickles, peppers, and tomatoes. Picked all ripe fruit and sprayed for disease before frost – this coming weekend will be a good harvest for most growers.”

Upstate

Kerrie Roach reports, “With some very cold nights last week in the upstate, the apple and peach crops took a significant hit. With extreme differences in topography, each grower has different severities of loss, but the overall consensus is not great. It will be another week to tell for sure on the apples and a little over a week to tell on the peach crop with certainty. One orchard recorded a low of 25 degrees F on the first night and 26 the following night. Night one was actually less damaging because of a persistent wind, where night two was calm and allowed the cold air to settle in. As we assess damages in the orchards, here is a great explanation of how it is done: https://extension.psu.edu/orchard-frost-assessing-fruit-bud-survival

Weekly Field Update – 3/29/21

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Coastal

Rob Last reports, “Strawberry crops continue to develop well with sustained flowering and fruit set. Early crops are ripening well with crops coming to market. Just a note of caution, the weather last week can be conducive to gray mold development, so fungicide programs are going to be key. Thrips are active in some crops too, so keep scouting. Melon transplants are going in the ground over the last week with development looking very promising. Peaches in the area are all but finished flowering with great fruit set. Finally, as we are looking at a cooler week for flowering fruit crops, keep an eye on the forecast temperatures to determine if protection is going to be required. Fruit and closed buds can tolerate cooler temperatures than flowers, but damaged flowers can increase gray mold development.”

Strawberries continue to develop well in the Coastal region. Photo from Rob Last.

Zack Snipes reports, “We have had pretty good weather as of late and it has really made things jump here.  Spring greens, onions, radishes, carrots, and strawberries are really pushing out hard.  I counted 57 green berries+flowers on one strawberry plant. If someone can beat that number, I will give you a Free Crop Handbook. The blueberry crop is looking great with a good fruit set on highbush varieties and tons of flowers right now on the rabbiteye types.  We planted around 30 citrus trees on Friday as part of a Specialty Crop Block Grant.  We have around 75 more to plant next year.  All in all we will plant somewhere around 40 varieties with varying scion and rootstock combinations.  We are looking at cold tolerance in both the lab and a field setting and monitoring for citrus greening.  We will plant everything from kumquat to grapefruit to finger limes.

Newly planted citrus trees at the Coastal REC this past week. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “Last week was pretty cloudy, but we had a couple beautiful days that reached the 80s. Though we’ve had a little bit of rain, the air has been thick with pine pollen. We’re seeing a few strawberries ripen but we’re still not at the point where we can open the U-Picks. We’re running a little behind where we’ve been in the past few years and I suspect all the cloudy weather we’ve had over the last month is partially to blame. I’m seeing a good bit of misshapen fruit, which is normal for the very first fruit that develop. This is usually related to pollination, but make sure you tissue sample to make sure boron levels are where they need to be. Watch out for the cool nights in the forecast later this week. We may need to cover. Spring planted brassica crops are looking good. Diamondback moths are showing up in places, especially near fields where a fall crop was grown through the winter, so be sure to destroy those fields once harvest is finished.”

Misshapen fruit are pretty common early in the season. Its usually related to pollination, but can be a sign of low boron. Tissue sample to make sure boron levels are adequate. Photo from Justin Ballew.
Spring planted brassicas are growing well and looking good. Photo from Justin Ballew.

Sarah Scott reports, “Peaches are progressing quickly with small fruit forming on early varieties. Georgia has reported plum curculio activity in the middle part of the state so orchards in the Ridge of SC can expect to see activity in about 2 weeks. Check the 2021 management guide for control options which include Imidan, Actara, Belay, and Avaunt. Strawberries farms are on track to begin picking regularly April 1. Spring greens are being transplanted as well.”

Pee Dee

Tony Melton reports, “Strawberries are ready to burst forth and there are already some fruit on Ruby June. Working to protect strawberries and peaches later on this week. A lot of summer crops will be going into the ground after Easter. Pickle growers are biting at the bit.  Most greens are just emerging. Cabbage is enjoying the weather and getting to what I call the whirl stage so hope we have no damaging winds to wring them off. Sweet potatoes slips are just emerging on the beds.”

Upstate

Are Hydrogen Peroxide Products Effective Fungicides?

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From Clemson Plant Pathologist Dr. Tony Keinath.

Should products with hydrogen peroxide, alone or combined with peroxyacetic acid, be used like fungicides on vegetables? It’s difficult to give just one answer to this question because there are so many different vegetables and diseases to consider. Here are a few important things to think about.

  1. Hydrogen peroxide/peroxyacetic acid has no curative activity against any vegetable disease. Yes, it might look reassuring to see the dead centers drop out of leaf spots on tomato. The pathogen, however, is still in the leaf, where pathogens are naturally designed to live. All leaf pathogens—bacteria, fungi, and water molds—will survive inside the treated leaves.
  2. Hydrogen peroxide/peroxyacetic acid has no (or a very short) residual activity or “staying power” on leaves after spraying. Conventional fungicides usually will last up to the minimum spray interval on the label, normally 7 days. Biofungicides also leave a residue on the leaves for at least a few days after spraying; there hasn’t been as much research on this as on conventional fungicides. The fact that labels like Oxidate recommend two applications per week suggests that the residue lasts no more than 3 days.
  3. Oxidate did not control powdery mildew on cucurbit seedlings in the greenhouse. (Details available at https://doi.org/10.1016/j.cropro.2012.06.009). There was absolutely no effect in any of four experiments. Unlike other fungi, powdery mildew grows mostly on the outside of the leaf, so it was completely exposed to Oxidate.
  4. The number of sprays per week needs to be considered when calculating the cost of hydrogen peroxide/peroxyacetic acid products. At $35/gallon and 1% solution, Oxidate costs $35/acre when sprayed twice a week at 50 gpa spray volume each time.

I recently tested Oxidate on kale affected with Alternaria leaf spot caused by the new species in South Carolina, Alternaria japonica. Oxidate (1%) was applied 2 days before harvest. Healthy leaves with no visible leaf spots were placed in sealed plastic bags with 100% relative humidity (RH) and stored at 41 F. for 1 week, then checked for disease symptoms. Based on two tests, 70% of Oxidate-treated leaves had Alternaria leaf spot, and 73% of water-treated control leaves did. That’s only a 5% improvement, and the difference is not statistically significant. Based on a kale price of $18/carton and 400 cartons/acre (for a once-over harvest), that’s an extra $359/acre.

Alternaria leaf spots that appeared a week after this kale was harvested and stored at proper storage temperatures. Photo from Dr. Tony Keinath

Oxidate might have some benefits sprayed immediately before harvest. After harvest, leaves aren’t exposed to more pathogen spores from the air, so the short residual time (hours) isn’t as limiting. Storing produce at less than 100% RH also might have made a difference with less disease overall.

For more information on Oxidate and vegetable diseases, see this list of trials with biofungicides approved for organic use with brief comments on efficacy: https://rvpadmin.cce.cornell.edu/uploads/doc_582.pdf.

Weekly Field Update – 3/22/21

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Join us this Wednesday (3/24/21) at 12:30 pm for a discussion on diamondback moth management in Brassica crops. It will be a relatively short meeting, lasting around 45 minutes, so tune in while you eat your lunch. Click here to register.

Coastal

Zack Snipes reports, “We got some needed rain but we got a lot of it in a short amount of time.  Winter peas and spring planted brassicas are looking good.  Tomato and squash are in the ground on some farms but because of the cooler weather and soil temperatures, really haven’t taken off yet.  I see a lot of brassica fields leftover from the fall.  These fields are harboring all of our insects and diseases that we will have to fight this coming season.  Mow these fields down and turn them under. Do not leave them.  I am seeing lots and lots of diamondback moths and black rot in these leftover fields.  Some more sad news this week from the Lowcounty as Mr. Adair McKoy, Sr. passed away this past week. Mr. McKoy was full of wisdom and had years and years of practical farming knowledge that he loved sharing with others.  Never did I visit him when I didn’t learn something new.  His love and care for the land was truly inspirational.”

Leftover collards from the fall that need to be mowed and tilled in. Photo from Zack Snipes.
A diamond back moth, one of thousands, I found in the leftover collard field. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “We had some cooler, wetter weather last week that slowed things down a bit in the fields. Several brassica fields that were planted in the fall and grew through the winter are right on the verge of bolting. If harvest is finished in these field, they need to be bush hogged and disked in as soon as possible to keep diamondback moths and any other caterpillars from breeding and making their way into spring planted fields. Strawberries are still coming along. There are lots of green fruit and a few are ripening here and there. I heard of the first few being picked in Lexington County last week. The weather conditions this week are going to be perfect again for Botrytis spore development, so don’t let up on spray programs.”

Fall planted mustard is just starting to send up flower heads. Photo from Justin Ballew
Lots of developing fruit on strawberries. Photo from Justin Ballew