All/multiple crops: Heat Stress and Vegetables: From Dr. Steve Reiners, Cornell University Vegetable Specialist: Near record breaking heat will have an impact on New York vegetable crops. In general, daytime temperatures that exceed 92°F and nighttime temperatures above 72°F can cause problems. The longer the heat lasts, the bigger the impact. Problems include:
Pollination issues in cucurbits – Heat favors male flower production over female flowers, resulting in fewer fruits, at least temporarily. It may also lead to drop of already set fruit. Bee flights/activity is reduced in hot weather which causes poor pollination and flower drop. In some cases, fruit will be distorted and crooked due to incomplete pollination. Cucumbers are especially sensitive to this disorder.
Tomato/Pepper flower drop – Flowers on these plants have a 48-hour window to pollinate. High temperatures can cause pollen sterility and flower drop. You may not notice the impact until 5 to 6 weeks later when yields are suddenly reduced for a period that aligns with the length of the heat wave.
Sweet corn yields – Although a heat loving crop, daytime temps over 95F can result in poor tip fill, missing kernels, smaller ears, and reduced yield.
Snap bean flower drop – Beans respond by dropping flowers. As soon as temperatures cool down, flowers will develop normally. Unfortunately, this may result in a split set, where some flowers set before the heat and others after. This is a big problem for one-time mechanical harvest.
Potato crinkle and heat sprouts – Distorted, yellow leaves often look like herbicide damage as chlorophyll is reduced. High soil temps can pause tuber development. Once growth resumes, rather than continued tuber expansion, tubers may sprout, producing above ground stems or chain tubers.
Poor color development – Although a little early for ripe field grown tomatoes, high tunnel growers may experience less red and more orange colored fruit. Some varieties may show more ‘yellow shoulders. Carrots and beets will also have duller colors.
Reduced sweetness – High temperatures increase respiration in plants, burning off accumulated sugars. This can result in bland tasting melons, sweet corn, and other crops. Radishes will develop a spicy flavor.
Premature flowering in greens – Spinach and lettuce will quickly bolt and develop bitter flavors prior to seeing the flower stalk.
Sunscald – Usually a problem with late season heat waves when loss of foliage is more prevalent, but any fruit exposed to direct sunlight can experience bleaching and browning of the exposed parts.
The most important thing to do during a heat wave is maintain an effective irrigation schedule. Unmulched fields can lose more than 5,000 gallons of water per day through evapotranspiration. Water stressed plants will close their leaf pores (stomata) and go in to survival mode, resulting in reduced yield and quality. If using overhead watering, try to irrigate first thing in the morning as evening or night irrigation can increase plant disease.
Alliums:
In most of our trapping locations in the North Country, the second flight of Leek Moth started last week. Leek moth caterpillars feed on allium foliage and scapes, and can bore into onion and garlic bulbs. “Windowpane” damage is visible on onion leaves from feeding within the leaf tubes, and frass is visible when the leaf is split open. If biological control is used for this pest, releases of Trichogramma brassicae should begin now, with repeated releases for the duration of the flight or until onions are harvested. UVM researchers have found that the egg parasitoid T. brassicae can reduce leek moth populations by up to 50%. Insecticide sprays should be applied approximately one week following peak flight. Lannate LV, Warrior II, and Radiant SC (conventional) and Entrust and DiPel (organic) are labeled for leek moth control in NYS. Entrust is the most effective organic pesticide for leek moth. If leek moth damage to onion foliage is widespread at harvest, it is recommended to top onions down to 1” above the shoulder before bringing in to dry and cure. Research has shown that topping onions in this manner does not impact storage quality, and reduces the number of holes in bulbs from caterpillars that may move down from foliage to bulb after harvest.
Brassicas: Diamondback Moth caterpillars were found this week feeding on cabbage, cauliflower and broccoli. Look for pale green larvae that are tapered at both ends with a few short, black hairs and usually wriggle aggressively when disturbed. They may even spin a strand of silk and dangle from the leaf. They also spin a loose “cocoon” of silk in which they pupate in. DBM are much different from Imported Cabbage moths which are usually lime green with blunt ends, very fuzzy in appearance and have a more distinctive, harder shell in which they pupate in. DBM feed very aggressively on many of the brassicas and can be difficult to control. Increasing the gallonage per acre upwards of 45 – 50 gallons per acre for better coverage can help and because many of the brassica leaves are very waxy, the use of a spreader-sticker may help stick sprays to the foliage. Products in IRAC Group 28 containing the active ingredient chlorantraniliprole (e.g. Coragen, Besiege or cyantraniliprole (e.g. Exirel) or Group 5 spinosyns (e.g. Radiant Entrust) are effective. The Group 11 or Bt’s (Bacillus thuringiensis var aizawi) including XenTari can also be effective, especially when larvae are feeding aggressively. Coverage is essential to Bt’s working and should be rotated with other insecticides.
Cucurbits: On July 1, Cucurbit Downy Mildew (CDM) was reported on cucumber in Lancaster County Pa. and on June 25th in Southeastern Michigan. Based on recent forecasts there very well could be the opportunity for spores to arrive in the area, riding on stormfronts. Look for bright yellow spots on cucumber leaves and if flipped over, a grayish purplish fuzz might be seen, especially early in the morning. If you suspect CDM, please contact your CCE ENYCHP specialist so we can confirm and report it on the CDM IPM PIPE website. Protecting crops right now with chlorothalonil (Bravo, Initiate etc.) will be important through the next 4-5 days with the expected showers in the forecast. Orondis Opti or Orondis Ultra and Ranman remain effective for CDM control for conventional growers and preventative applications of copper for organic growers. For more control options click here.
More Gray Squash Bug eggs(tiny, copper colored beads) were found on multiple farms again this week so egg hatch has probably already been happening and that is the time when you want to target your control measures. Assail or Arvida (acetamiprid) or Endigo (24 hour REI) both have good residual. Warrior or several other pyrethroids can also be effective. For organic producers, multiple applications of azadirachtin plus PyGanic at the higher rates can be effective, but only on small nymphs. Make sure to penetrate vines and cover undersides of leaves for best control.
In discussions with Cornell Weed Scientist Lynn Sosnoski, research in her field plots indicated that injury from post emergent applications of Sandea or halosulfuron containing products at the 2-leaf stage of growth caused unacceptable damage and waiting until plants were older – 5 leaves or more reduced injury and did not have any major impact on yields. I mention this because the label indicates that it can be applied when “plants have 2-5 true leaves but before the first female flowers appear”, but holding off may be safer for the plants, but weeds may become to big for the herbicide to work. In that case, a shallow cultivation on a good hot, dry day a day or two prior to a Sandea/Profine application to try and kill any of the larger weeds might be worth considering. Then applying Sandea/Profine can re-establish the herbicide barrier. Grass weeds that come through can be dealt with fairly easily with several post-emergent grass herbicides that are labeled (clethodim or sethoxydim). Do not tank these grass herbicides with a post emergent Sandea/Profine application.
Nightshades: All stages of Colorado potato beetle CPB (adult – small larvae) can now be found especially in potato stands. Increasingly, organic producers using Entrust (spinosad) to control CPB are reporting decreased efficacy. CPB is notorious for developing insecticide resistance especially with repeated use of an insecticide, year after year. Resistance management can be especially challenging in organic production where there are few effective insecticide options. Azadirachtin and Pyrethrin products such as Azatin, AzaGuard, Molt-X, Aza-Direct, Ecozin Plus, Neemix, Azera and Pyganic) can be effective. Apply at the highest labeled rate starting when small larvae are first observed. Follow label directions for tank mixing and spray water pH adjustment to below pH 7 to maximize efficacy. There are practical and effective options developed for mechanical controll of CPB; consider investing in devices such as a flamer or beetle sweepers.
Sweet corn: In the Hudson Valley, early sweet corn that was under row cover is now maturing and harvest has begun. Corn ear worm pressure remains elevated in multiple locations calling for a 4-day insecticide spray interval in silking corn. Corn that is earing up could also use some irrigation to ensure optimal tip fill. Early corn that suffered from prolonged wet soils might be at more risk due to poorer root development. Scouting surveys out of New Jersey are reporting Fall Armyworm (FAW) populations are increasing so paying attention to younger corn and the trap catches reported in our newsletters will be important. FAW can feed and damage young corn – look for large, ragged feeding holes in younger corn with lots of “sawdust” looking material, especially in the tassel area.
Miscellaneous:
Pre-Harvest Intervals (PHI) and Re-entry Intervals (REI): Please, please, please make sure you read the labels for all pesticides (organic or conventional) before applying them! Not only does it ensure your safety, your workers safety and the safety of those purchasing the product, but it is also the law, according to the labels. For example, someone who might want to use Dimetric herbicide (metribuzin or the old Sencor) on potatoes right now but wants to dig potatoes lets say the end of July for new potatoes, needs to pay attention to the label because the post harvest interval for that product is 60 days! So just please pay attention to the label and the PHI and REI information. If you can’t find it on the label, call your local vegetable specialist or your chemical supplier and ask them for help.