2022 PA Vegetable and Berry Current Issues for June 7

Regular scouting for diseases will be even more critical with the anticipated wet weather this season. When deciding whether or not to apply a fungicide in advance of rain, consider the rainfast period of the product (check the label). Applying fungicides when the leaves are dry is essential to prevent excess run-off. Also include adjuvants recommended on the label to help the product adhere to the plant surface. One to two inches of rain will remove half of the residue for protectant fungicides (such as captan, thiram, mancozeb, or chlorothalonil). To protect newer growth, shorter intervals between sprays may be needed. Please pay attention to the total number of applications and amount of active ingredient that can be applied in a season and try to plan, so you do not run out of options when you need them most.

High Tunnel Production

While growers are focusing more on field production, high humidity diseases such as leaf mold are developing in high tunnels in part due to increasingly dense plant canopies. The pathogen that causes timber rot on tomato or white mold on snap bean has also been observed on peppers. Cool, wet weather favors the development of this fungal pathogen, Sclerotinia sclerotiorum. It has a wide host range that includes almost all crops commonly grown in high tunnels.

Effective fungicides and crop rotations as management options are limited, so reducing inoculum through sanitation is important. Removing infected plant tissue before the sclerotia form, thus preventing them from dropping to the soil, is critical; they can survive for years without a host. Magnesium deficiency in high tunnel tomatoes is a common sight this time of year as the crops are setting fruit.

This week, there are striped cucumber beetles in various cucurbit crops, including high-tunnel cucumbers and field-grown squash. Adults are attracted to volatiles from cucurbit cotyledons—an aggregation pheromone emitted by males, combined with volatiles from frass and plant-feeding. Females lay eggs at the base of plants, and larvae feed on roots. Minimizing the immigration of these overwintered adults will go a long way toward reducing populations later in the season.

Figure 2. Striped cucumber beetle. Photo: N. Sloff, Penn State

Neonicotinoids are effective but are systemic and are highly toxic to bees. Limiting neonics to treated seed such as FarMore FI400, which includes the neonic thiamethoxam, keeps residues in nectar and pollen at very low or non-detectable levels. Very low rates applied to transplants may also reduce residues to which bees are exposed. In addition to feeding on crops, these beetles can be particularly problematic through their ability to spread the bacteria that cause cucurbit bacterial wilt, particularly in cucumbers and melons. Make sure to scout for these pests and be prepared to manage them if necessary. Once bacterial wilt has affected the crop, there is no rescue treatment to address it, so manage beetle activity to prevent transmission.

Field Production

Monitoring for fall armyworm and corn earworm via pheromone traps has begun across much of Pennsylvania. So far, very few moths of either species have been captured. We will be providing weekly updates on these trap catches as the season progresses to help guide spray decisions for growers who will use insecticides to manage them. If you have planted Bt sweet corn with the VIP traits for corn earworm, you will likely see minimal damage from caterpillar feeding but may still need to scout and treat for other pests, such as sap beetles or flea beetles. If you have not planted VIP corn, keep an eye out for our reports as your corn approaches tasseling, as this is when management should begin.

Damage from thrips continues to show up in numerous crops. Common species in vegetable crops in our area include Onion thrips, Eastern flower thrips, and Western flower thrips. Insecticide options will vary with the crop. In tomatoes and onions, the spinosyns materials (Radiant, Entrust, which is OMRI-labelled) have been the most common insecticide used against thrips, but resistance is suspected for some populations. Diamides (such as Harvanta) are labeled for thrips on tomatoes, and multiple neonicotinoids and pyrethroids are also labeled. Also, continue to scout for spider mites.

Figure 3. Sap beetle adult. Photo: M. Price

Sap beetles have been observed in several crops. Adults overwinter in wooded areas and protected locations. In field settings, they tend to build where adults and larvae can feed on "free sugars," often unharvested ripe berries, cantaloupes, and other fruit. Populations can then move into sweet corn, which can be very difficult to control. Farms with both strawberries and sweet corn should avoid having a population of sap beetles build up in their berry crop. Compost piles and areas where produce is discarded are also where sap beetle numbers multiply. When we find sap beetles in sweet corn, we often find lots of larvae in a single ear, even in crops that have been sprayed. Sap beetles and mycotoxins - Aspergillus and Fusarium - have a complex interrelationship. Sap beetles belong to a family of beetles that transport fungal spores, and the interaction of these fungi with the plant tissue may be important for the insect's development.

Cucurbit downy mildew is currently reported as far north as eastern North Carolina on cucumber and in coastal South Carolina on cucumber (Cucumis sativus) and acorn/yellow/summer squash (Cucurbita pepo). We are learning that cucurbit downy mildew has two host-adapted clades. Clade 2 more frequently affects cucumber and cantaloupe (Cucumis melo) and affects these crops in our region every year. In the past seven years, downy mildew has been first reported on cucumber as early as 23 June and as late as 22 August. This is compared to Clade 1, which affects squash, pumpkin (Cucurbita maxima), butternut squash (Cucurbita moschata), and watermelon (Citrullus lanatus). There are many years when this clade/strain of the pathogen does not affect this region or shows up late enough in the season that we do not need to apply fungicides for management. Remember that cucurbits are susceptible to downy mildew at any growth stage, from seedlings to mature plants, and regular scouting is essential. Fungicides are currently our primary management tool.

Figure 4. Progression of downy mildew lesions on cucumber starts light yellow/ chlorotic but becomes more water-soaked and tan. Photo: B.K. Gugino, Penn State

Berry Crops

Strawberry harvest is well underway, and an assortment of issues are creeping in. Problems vary with the farm and sometimes depend on nursery source and variety. Issues include Neopestalotiopsis mainly in plasticulture 'Chandler' (see Be on the Lookout for Neopestalotiopsis on Strawberries), Phytophthora crown rot in plasticulture 'Flavorfest,' for which it is getting too late to treat for this year, and fruit anthracnose on an assortment of varieties (see Strategies for Effective Management of Botrytis and Anthracnose Fruit Rot in Strawberries).

Both cyclamen mites and spider mite numbers have picked up in strawberries across the state. Leaves of strawberry plants infested by cyclamen mites will appear stunted or crinkled, and leaving the mites uncontrolled can result in dwarfed fruit or reduced fruit set. At this point, it will be challenging to get miticides into the crown area for cyclamen mite control. As noted in the last update, the next good window of opportunity for treatment of this pest is at renovation for matted-row plantings. Spider mite feeding will cause leaves to become bronzed or yellowed and may also be accompanied by webbing if numbers are high enough, as mites use silk to disperse to new plants. Spider mite populations increase rapidly in hot, dry weather. Consider applying a miticide to control two-spotted spider mites, ensuring good spray coverage to improve efficacy. If you are managing other pests with insecticides (which do not control mites), choose the most selective and effective product available to avoid eliminating natural enemies of pests that can help control both types of mites.

Figure 5. Sunscald causes a bleaching of berries on the upward-facing portion of the fruit. Photo: K. Demchak, Penn State

Both ripening and green strawberries have suffered sunscald during the hot days we had following cool, cloudy weather. Sunscalded strawberries first appear bleached and soft, but after a few days have passed, the damage could be mistaken for a fruit rot as tan sunken areas develop where the fruit tissue has died. At this point, sunscald can be differentiated from fruit rots because symptoms are only on the upward-facing portions of the fruit and are more common on berries facing South.

Some growers report smaller-than-usual strawberries, which may be due to dry conditions as the berries were sizing. However, in other instances where some or all of the primary blossoms were damaged by frost early in the season, secondary or tertiary fruit comprise most of the harvest. While some compensation in size occurs once the primary blossoms are lost, the secondary and tertiary berries will never be as large as the primary berries would have been.

Figure 6. Exoskeletons of tiny spongy moth larvae found in dead blueberry blossom clusters and their frass. Their feeding on pedicels resulted in blossom death. Photo: K. Demchak, Penn State

In the previous update, we discussed the presence of spongy moth (Lymantria dispar, previously known as "gypsy moth") being present in high numbers on blueberries. In a relatively uncommon occurrence, early instar caterpillar feeding resulted in damage to flower pedicels, causing the death of individual flowers and sometimes the entire flower cluster. This damage could have easily been mistaken for a blossom blight caused by botrytis, Phomopsis, mummy berry, or anthracnose. Once the blossom cluster was pulled apart, some webbing, the tiny larval exoskeletons, and frass could be found. A similar situation was documented in Rhode Island in 2017.

The best time to treat this pest is when caterpillars are still small and in their early instars when the Btk strain of Bt (Baccillus thuringiensis var. kurstaki) is effective. Earlier instars can be differentiated from later instars by their black head capsules.