2022 PA Vegetable and Berry Current Issues for July 19

Heat and drought stress has taken its toll, especially on crops with limited access to steady irrigation or that are non-irrigated. In some regions, corn maturity has been delayed, and pumpkins are slower growing. Blossom end rot and physiological leaf curl have been reported on tomato.

Field Production

Reports of downy mildew on cucumber have been rapidly expanding over the past week, with confirmations in NH, MA, CT, southeastern NY, NJ, OH, and most recently in MD, DE, and Ontario, Canada. The increase in sources of inoculum across the region, along with the much-needed rains Sunday and Monday, placed much of PA at risk for downy mildew on cucumber and cantaloupe, especially if effective fungicides are not protecting the crops. Symptoms resulting from this most recent rain event will become visible within 7 to 10 days. Powdery mildew is being reported on early planted cucurbit and squash crops. Bacterial wilt is developing in fields with higher populations of cucumber beetle that transmit the bacterial pathogen.

Figure 1. Cucurbit downy mildew risk map for Monday, July 18, 2022. Regions in red, orange, and yellow are at high, moderate, and low risk of pathogen infection and disease development, respectively.

Onion harvest is well underway. For fields with bacterial disease issues, keep in mind that once the neck is dried down, the bacteria can no longer move from the leaves into the bulb. So thoroughly field curing and drying the onions down is essential to maintain post-harvest marketability. Post-harvest conditions can also affect the development of black mold. Black mold is the black soot-like fungal growth on and between the bulb scales. It is caused by the fungal pathogen Aspergillus niger, which is common in the soil and crop residue and affects many vegetable crops. It is favored when bulbs remain hot under high relative humidity (>80% RH), or there are fluctuations in temperature (e.g., coming out of cold storage) that result in the formation of condensation on the bulbs while in the bins, followed by exposure to high temperatures. Reducing exposure to high temperatures and storing at low humidity will help manage black mold.

Figure 2. Characteristic Cercospora leaf spot lesions on a red table beet leaf. Photo: Beth K. Gugino, Penn State

Cercospora leaf spot is being reported on beets. Cercospora causes circular tan lesions surrounded by a dark purple border that is easily recognizable. The spores are splash-dispersed similar to those of early blight or Septoria leaf spot on tomato. Warm temperatures and leaf wetness favor disease development. Weedy hosts, including lambsquarters and pigweed, can serve as reservoirs of the pathogen. Fungicide resistance to FRAC 11 fungicides has been a documented problem in NY, where there is significant acreage of processing beets. Rotating among FRAC codes is recommended for resistance management. Based on trials in NY, organic recommendations for disease management include Cueva tank mixed with Double Nickel LC or LifeGard, which have been as effective as conventional fungicide programs.

Insect Updates

Sweet corn moth pests have decreased since June. Scouting and management efforts can be concentrated on tasseling and silking corn, which is highly attractive to these moths. If doing your own monitoring for corn earworm via pheromone traps, be sure to identify the moths caught in traps correctly. 2022 has been a big year for spongy moth activity in Pennsylvania, which is typically a forest pest, and male spongy moths have found their way into corn earworm traps throughout the central part of the state. Both species can be light in color, but the shape of the antennae clearly distinguishes the two. Corn earworm will have slender antennae, whereas spongy moths will have bushy antennae. In some parts of the state, sap beetles have moved out of strawberries into sweet corn, which can cause ear damage. If seeing damage from sap beetles and not from caterpillars, opt for a pyrethroid to manage them.

Figure 3. (Left) Adult corn earworm moth caught in monitoring trap. (Right) Adult male spongy moth. Photos: left, Karly Regan, and right, Tom Butzler, Penn State

Squash bugs are active in pumpkin and squash. Look for egg masses and young nymphs on the undersides of leaves. The early instars, which range in color, stay clustered on or near the egg mass for a while. Insecticides are most effective before canopy closure. Squash bugs are the vector for a pathogen called yellow vine decline. Recent data from Virginia Tech suggests that Sivanto and Beleaf are effective and help conserve a common parasitoid of squash bug. These products can also provide good control of striped cucumber beetles, another insect pest that spreads a pathogen, resulting in bacterial wilt. Squash vine borer is also active.

Figure 4. Squash bug egg masses on pumpkin leaf. Photo: K. Regan, Penn State

Berry Crops

Spotted wing drosophila is present in warmer regions of the state but is also starting to be detected in cooler areas. Information on insecticide efficacy, and a table that includes allowable materials for berry crops with pre-harvest and re-entry intervals, can be found in the article Spotted Wing Drosophila: A 2021 Update for Berry Growers.

We are close to the time of year when blueberries, matted-row strawberries, raspberries, and blackberries can be sampled for leaf nutrient analysis. With all berry crops, the correct leaves to test are the most recently fully expanded ones. Timing for blueberries corresponds to what would be the last week of harvest for a mid-season variety like ‘Bluecrop’; other varieties should be sampled at the same time by the calendar even though they may be at a different point in their harvest season. Matted-row strawberries should be sampled after renovation when sufficient foliage has grown back, and leaves from primocanes of summer-bearing raspberries and blackberries should be sampled between Aug 1 and Aug 20. For more information on how to sample berry crops correctly and in a way that will result in useable results, see the article Tissue Nutrient Analysis for Berry Crops: Getting the Most for Your Money. A sampling at the wrong time of the year or choosing the wrong leaves can lead to incorrect conclusions about the plants’ nutritional status.

Figure 5. Phytophthora crown rot symptoms on ‘Flavorfest.' Photo: K. Demchak, Penn State

Thanks to the work of folks in the Plant Disease Clinics at Penn State and the University of Delaware, we now know that the crown rots affecting ‘Flavorfest’ over the past couple of years were caused by several different disease organisms, all of which would be categorized as “water molds,” Pythium, Phytophthora, etc. As mentioned last week, after harvest and renovation is the time to treat June-bearing strawberries with products such as Ridomil or Orondis Gold if these diseases are known or strongly suspected to be present, such as when strawberries are grown in wet fields.

Finally, as you choose fields for new plantings of plasticulture strawberries being planted this summer, select fields that have been out of strawberry production for as long as possible. Most growers who have come back into fields that have had strawberries several times, even when allowing three or more years between plantings, have been disappointed in plant performance. In contrast, those who have been able to lengthen rotations report fewer problems overall. New ground does best.