2021 PA Vegetable and Berry Current Issues: July 21

In some areas, the stagnant hot muggy air mass that fueled numerous severe thunderstorms has delayed planting, caused variable levels of crop damage, and exacerbated diseases and crop issues associated with rain and flooded soils. The break from the daily storms this week will hopefully facilitate some drying.

Field Production

Continue to be on the lookout for downy mildew on cucumber and cantaloupe. Most recently there have been new reports in southeastern Pennsylvania and New York as well as around the Great Lakes in Ontario, Canada, and Michigan. Powdery mildew is also starting to show up on cucurbit crops. It is important to scout cucurbits crops by cultivar or at least start scouting the cultivars that are most susceptible. When scouting be sure to look at the underside of the leaves and petioles where symptoms are likely to first develop. Fusarium stem and crown rot are being reported on pumpkin and Phytophthora blight is being reported on cucurbit and pepper crops.

Bacterial disease issues are being reported on numerous crops from onions to tomatoes to peppers to brassicas. It is not surprising given the high temperatures and frequent rain events that are ideal for spreading bacterial pathogens. Once bacterial diseases are observed in the field, they can be very challenging to manage. The primary go-to is fixed copper often tank-mixed with mancozeb. The use of plant defense resistance inducers such as Actigard are most effective when incorporated into a program early before symptoms are observed. Take notes on which cultivars are most affected and consider planting alternative cultivars in the future. This is particularly true for peppers which vary considerably in which races they carry resistance to. Be on the lookout for copper resistance.

There continue to be no reports of late blight in the region however there have been a couple of reports of buckeye rot. This is caused by a different species of Phytophthora than one that causes late blight, but the symptoms can look similar. Buckeye rot will typically develop on the leaves and fruit closest to the ground and will produce little to no spores, so it does not spread rapidly like late blight. Early blight as well as Septoria leaf spot on tomato. These commonly develop on the lower leaves with the onset of fruiting as the plants reallocate resources from the lower leaves into fruit production. When applying fungicides adequate coverage is important because many products are either strictly protectants or are only locally systemic.

Wirestem is a disease of young brassica/cole crops such as cauliflower, cabbage, and broccoli. It tends to be more problematic in fall versus spring-planted crops due to more prevalent warm and wet soils. It can also be worse in soils with higher organic matter that provide a food source for the fungal pathogen Rhizoctonia solani and in heavier textured soils. It causes lesions along the seedling or young transplant stem that eventually girdle the stem and severely restrict root development. Over-fertilizing transplants during production and after transplanting can make them more susceptible to wirestem. Consider applying fungicides before or shortly after transplanting.

Figure 2. Girdling lesions on cauliflower stems caused by wirestem. Photo: Beth K. Gugino, Penn State

Two migratory moths, corn earworm (CEW) and fall armyworm (FAW), are increasing. Tasseling and silking corn will be highly attractive to these moths. CEW eggs are laid on silk, individually, hatch in 2-3 days, and neonate larvae bore through the silk channel and into the ear tip within one to a few days. Insecticide control requires contact with the very young larvae before it moves into the ear.

FAW lays eggs in clusters on leaf tissue, including the flag leaf. Larvae feed on leaf tissue in whorl stage corn but will rapidly tunnel into the ear from multiple places. You can distinguish the larvae by looking at the head capsule: CEW tends to have a lighter color head capsule, and FAW has a darker head capsule with a more pronounce inverted Y marking made from the color along the edge of the plates that make up the head.

Figure 3. Head capsule of Corn earworm (left) and fall armyworm (right). Photo: G. Dively

Figure 4. Corn earworm (left, photo H. Fescemeyer) and fall armyworm (right, photo R. Bessin).

Both moth species, which are in the same family (Noctuidae) have resistance to pyrethroids. Other options include those from IRAC group 5 (Blackhawk, Radiant) and IRAC group 28 (Coragen, Vantacor). The group 5 options have low bee toxicity, and Vantacor can be obtained in smaller quantities. However, these group 5 or 28 options will not control sap beetles, silk-clipping beetles (adult stage of western corn rootworm), or stink bugs. Another migratory noctuid, the yellow striped armyworm (YSAW), has been causing defoliation or fruit damage in tomato and potato in previous years. Although we have not had reports of YSAW so far this year, now would be the time to check for early signs of defoliation or direct damage to tomato fruit.

Squash bugs are active in pumpkin and squash. Look for egg masses and young nymphs on the underside of leaves. The early instars, which range in color, stay clustered on or near the egg mass for a while. Sprays can be effective, but contact is difficult as the canopy closes. Sprays are most effective prior to 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. Squash vine borer is also active.

Figure 5. Squash bug adult, hatching nymphs, and yellow vine decline. Photos: N. Sloff (upper left), T. Kuhar (lower left), S. Fleischer (right).

Berry Crops

Spotted wing drosophila is the main pest of concern for berry growers at this time of year. For updated info on insecticide efficacy and a table with that includes allowable materials for berry crops with pre-harvest and re-entry intervals, see this recent article: Spotted Wing Drosophila: A 2021 Update for Berry Growers

Some growers are reporting issues with high populations of yellow jackets in pick-your-own blueberry fields and fruit damage to day-neutral strawberry fruit. This is a serious concern for pick-your-own customers and other harvesters, as yellow jackets can sting multiple times, may have large nests nearby, and can be very aggressive when disturbed. It may take a multi-pronged approach to achieve control, and of course, protective clothing should be used before any control method (destroying underground nests, baiting and deploying traps, or spraying in the field) is undertaken. More information on yellow jackets and wasps can be found here: Tree Fruit Insect Pests - Yellow Jackets and Hornets. Some of the sprays mentioned for SWD control in the link provided in the previous paragraph for SWD management (Mustang Maxx, Brigade or Bifenture, and malathion) would be expected to help with this problem in addition to helping manage SWD.

APHIS is proposing to issue permits related to the release of a tiny wasp parasitoid as a biological control agent for spotted wing drosophila. A public comment period related to this proposed action is open from now through August 16, 2021. Comments may be submitted by visiting Regulations.gov and then clicking on the blue comment button in the upper left portion of the page (red circle in the image below). By clicking on “View More Documents” (yellow square in the image below), you can download the Environmental Assessment which provides more details about the parasitoid, and how and why it was chosen. Success is far from certain, but this is one step towards potentially decreasing SWD issues longer term.

Figure 6. Document ID: APHIS-2021-0021-0001

The correct time of year for sampling berry crops for a nutrient analysis is now or coming up shortly. For more information on how to sample these crops correctly and in a way that will result in useable results, see 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.