Vegetable Notes 2024 Vol. 36:19

Onions are mostly curing now, as growers rushed to get them out of the field before Hurricane Debby dumped (or threatened to dump) big rains across the state this week. Storms and rain also threatened our climate change-themed Twilight Meeting last week at Bardwell Farm, but we had a good crowd turnout in the end—thanks to those who came! Harrison shared his experience getting his feet wet (pun intended) using soil moisture sensors. He bought an automated irrigation system with financial assistance from NRCS, but struggled to get it setup in time to use this season. He found that installing just 2 soil moisture sensors in each high tunnel (at the top and bottom of the crop rooting zone) and using the handheld reader to check them each week provided plenty of data to help him fine-tune his irrigation scheduling. This was critical for him because the soil in the tunnels is infested with Phytophthora capsici, and by limiting the amount of water in the soil, he is able to grow a forest of multi-colored bell peppers despite having this disease present.

Our next meeting is next Tuesday, August 13, at the UMass Crop and Animal Research Farm where the Vegetable Team and colleagues from around UMass will share their ongoing field research with the public. This year our team will have cucumber, basil, and lettuce variety trials to showcase, and we’ll also discuss corn earworm population dynamics. And it’s always fun to see what is happening across the different research labs at the University! One other note about events: our sunflower meeting at Siena Farm later this month is canceled, but we are replacing it with a workshop on dahlias later this fall. We hope to have the details out by next week—keep an eye out!

Pest Alerts

Tomato fruitworm (aka corn earworm) was observed tunneling into high tunnel tomatoes in Hampshire Co. this week. This pest, which primarily feeds in corn, will also attack tomatoes, particularly if moth numbers are high and fresh corn silk is scarce. Small larvae enter the stem end of fruit and develop inside, emerging later and much larger from the fruit wall. If control is warranted, use selective insecticides, such as Bt (e.g., Xentari Dipel) to avoid disrupting natural enemies that control secondary pests, such as mites and aphids. Timing of applications is key since larvae are protected once they enter the fruit.

Anthracnose was observed in a field in Hampshire Co. this week. Anthracnose is a fungal disease that causes round, sunken lesions on tomato and pepper fruit. The lesions eventually develop concentric rings of dark fungal fruiting bodies, giving them a fuzzy black appearance. This disease affects ripe fruit only, and we most commonly see it in crops that are being underharvested. Harvest thoroughly to reduce inoculum, then practice at least a 1-year crop rotation out of solanaceous crops. This fungus can be carried on seed—hot water seed treatment can effectively eliminate the pathogen from the seed.

Stemphylium leaf spot, or gray leaf spot, was confirmed last week on tomato and another case is suspected this week. This is a relatively new fungal disease of tomato in the Northeast. The pathogen forms brown leaf spots that develop a gray appearance when the fungus produces spores. It can look very similar to Septoria leaf spot. See the article in this issue and the Tomato Disease Control section of the New England Vegetable Management Guide for more information.

Pepper maggot is causing damage now in pepper crops. Pepper maggot feeding damage often leads to secondary rots, and infested fruit are often culled in the field or packhouse without growers knowing the cause of the damage. Open up rotting fruit, or fruit that fills with water during washing, and look for 1 cm-long larvae inside. Remove infested fruit from the field and destroy (make sure the fruit isn’t left in a cull pile for the pest to complete its life cycle). Growing on black plastic and covering aisles with landscape fabric can break the pepper maggot life cycle—the maggots will drop to the soil to pupate but will die if they are prevented by the landscape fabric from entering the soil. Pepper maggot can be effectively managed using insecticides, but they must be applied at the first sign of pest presence.

Sweet corn

European corn borer (ECB): Trap counts are low, and second generation ECB caterpillars are causing feeding damage in crops now. This generation feeds on sweet corn but also a wide range of other crops, from peppers to garlic. ECB damage was suspected this week in dahlias—stems and leaves were turning brown and dying back, and slicing open them stems revealed insect tunneling.

Corn earworm trap counts are still relatively high, with most farms on a 4-day spray schedule but a few on a 3-day schedule. Corn earworm (also called tomato fruitworm) will also feed on tomato fruit, so if trap counts are high in your area, it's worth scouting your tomatoes for damage too, and spraying if necessary.

Fall armyworm (FAW) continues to be caught in low numbers in some locations, with 4 out of 15 trapping locations reporting moths this week. Caterpillars are actively feeding in the latest corn plantings now, which are at whorl stage. A good time to apply a pesticide is when tassels have just fully emerged, to catch the caterpillars before they migrate down from the whorl and tassels into the ears.

Harvest and Curing Tips for Onions

Lots of farms are done harvesting onions already, ahead of the rain expected from Hurricane Debby, so greenhouses and barns are filling up with tables and crates of curing onions. Deciding when and how to harvest onions, then where and how to cure them can be challenging. When are they really ready to be pulled? Is the weather too wet or hot, or is the field too weedy to field cure? What should I do if there is a lot of foliar disease in my crop? The recent cool August temperatures are closer to ideal than normal for curing, but the upcoming rain will make the curing environment more humid and will prevent field curing. Here are a few tips, originally from University of Minnesota Extension:

Harvest

In order to maximize storage life, onions need to be harvested while the onion foliage is still partially (30-40%) erect, which is unfortunately long before maximum yield is attained (when tops are completely down and dry). Yields may increase 30-40% between the stage when tops begin to go down and when the leaves are fully down and dry, so it is tempting to leave onions in the field as long as possible. The optimum time for harvest, therefore, must be a balance between highest yields and reduced bulb storage quality. From UGA Extension: “Maturity is best determined by pinching the neck of the growing onion. Necks of immature onions are stiff, while necks of optimally mature onions are soft and limber. When the necks are so weak that they cannot support the tops, the onions are over-mature. Simply observing the percentage of tops having fallen over is not a true indication of maturity, since the tops can be knocked over by strong winds, rain or become limp from lack of moisture.”

Digging and windrowing

To facilitate curing onions for harvest and storage, onion rows are undercut and lifted and, if the onions will be cured in the field, they are windrowed. Rod-weeder diggers and knife undercutters are most often used. Onions are commonly dug and windrowed with tops on – tops can be layered on top of bulbs to protect the bulbs from sunscald. After field drying has occurred, the onions may be topped and placed in storage buildings or moved to a curing space to continue drying down.

Curing

The goals of curing onions are to properly dry down the outer bulb layers to protect the onion bulb and to dry down and seal any wounds that may have occurred during harvest. Onions can be cured in the field, in open sheds, or by artificial means before or in storage. Adequate curing in open sheds may require 2 to 4 weeks, depending on the weather, with faster curing occurring in hotter, dryer weather. Optimal curing conditions, which also result in the best skin color, are 75-80°F and 70-80% relative humidity, with good air circulation. Onions are considered fully cured when the neck is tight and the outer scales are dry and make a rustling sound when handled. When you pinch the neck between your fingers, it should feel dry and not juicy and slippery. This condition is reached when onions have lost 3-5% of their weight. If not adequately cured, onions are likely to decay in storage. The most common form of decay is Botrytis neck rot, which occurs at the top (or “neck”) of the bulb.

Topping

Most onions are cured with tops on and topped before being moved to storage. Remove tops when they are totally dry, or, only remove the dry portion. Cutting through any portion of the top while it is still green or moist allows for entry of bacteria and fungi and most commonly can result in excessive Botrytis neck rot in storage. When all or a portion of the onion top is left on, the remaining tops are removed during grading and packing. Topping is either done by hand or with mechanical roller toppers.

Here are our low-tech recommendations for curing and storage in New England: A greenhouse or hoophouse provides a good environment for curing, where temperature, airflow, and moisture can be somewhat controlled. Be sure to keep the temperature in the house below 85°F, which will probably require turning on fans and/or leaving sides and doors wide open. Consider using shade cloth over the house to help moderate temperature. Curing can be done in the field, but it is harder to achieve good conditions for curing in an uncontrolled field setting. Avoid field curing onions if rain is forecasted and, if it does rain, let the onions dry fully before handling. Handling bulbs when they are wet can facilitate the spread of fungal and bacterial diseases that can further develop in storage. Weedy fields may be excessively moist and air circulation may be limited; these conditions are not suitable for curing, so bring onions inside to cure. Temperature and sun are also factors to consider—sunshine and temperatures in the 80s will enhance the bronze color in the skins, but extremely hot sun and temperatures in the 90s can cause sunscald. Onions curing on a sandy soil will heat up more quickly than those curing on a heavier soil.

Storage

To ensure maximum storage life, onions must be promptly stored after curing. Get them out of the sun, as exposure to light after curing will induce greening of the outer scales. The optimum temperature for long-term storage of onions is 32°F with 65-70% relative humidity, but it is important to bring them down to this temperature slowly. In fact, holding onions in a barn or garage so that they cool along with the average outdoor temperature in late summer and fall works quite well. Avoid cooling bulbs to well-below the average daily temperature because they will draw moisture from the warmer air, which can lead to disease development. If you are selling the onions within a couple of months, keeping them in an un-insulated barn is fine. An insulated storage room is needed for longer-term storage.

Quick Tips for Best Quality

• Be sure onions are well-dried and necks are tight (i.e. the tissue does not slide when you roll the neck between your fingers) before topping. Bacterial diseases and Botrytis neck rot can move through green tissue into the bulbs. These diseases do not move through dry tissue.
• Leave 2-3 inches of neck on the bulb. This increases the distance from the cut surface to the bulb for these pathogens to travel.
• Minimize mechanical injury during harvest & topping. Reduce drops to 6” and pad sharp surfaces. Bruises provide direct entry points for diseases to get started.
• Grade out damaged onions before putting them into storage. Damaged bulbs give off moisture, which is favorable for development of diseases in storage.

--Written by the UMass Vegetable Program

Gray Leaf Spot on Tomato

Gray leaf spot of tomato has become more common in the Northeast in the last several years. This disease is caused by several species of the fungus Stemphylium. Stemphylium lycopersici (= S. floridanum), S. solani, and S. botryosum (AKA Macrosporium commune), have all been reported to cause the disease on tomatoes in North America. These species do not cause Stemphylium leaf blight of onion, which is associated with the species S. vesicarium.

Symptoms begin as small brown lesions that may or may not have a yellow halo. Lesions may turn tan as they enlarge and may tear in the center or appear gray due to sporulation of the fungus. Lower leaves are often affected first. Severely affected leaves may turn yellow or brown and defoliate. Symptoms are seldom seen on petioles or stems, and fruit is not affected. The symptoms closely resemble those of Septoria leaf spot, but Septoria lesions are often observed on stems and petioles.

Stemphylium species survive in infected crop debris and solanaceous weeds. They may also be seedborne. The spores are spread by wind and splashing water. The optimum temperature for spore germination and disease development is 75-80°F. Symptoms can appear as soon as 5 days after infection.

Gray leaf spot management options include proper plant spacing and removal of lower leaves to increase air circulation. Avoid overhead watering if possible. Control weeds and remove volunteer solanaceous plants from fields. Remove or plow under infected crop debris and rotate away from solanaceous crops for at least 3 years. Several resistant varieties are available: see https://www.vegetables.cornell.edu/pest-management/disease-factsheets/disease-resistant-vegetable-varieties/ for a complete list.

Fungicides labeled for gray leaf spot management include chlorothalonil (Bravo), mancozeb and zoxamide (Gavel), cyprodinil and difenoconazole (Inspire Super), trifloxystrobin and fluopyram (Luna Sensation), azoxystrobin and benzovindiflupyr (Mural), and copper (Nu-Cop), among others. Fungicide resistance has been observed, so be sure to rotate active ingredients.

--Written by Angie Madeiras, UMass Plant Diagnostician