2022 PA Vegetable and Berry Current Issues for August 30

The Northeast Regional Climate Center recently published a map (Figure 2.) showing the percent of normal precipitation for the first half of August across the northeast. While much of the state was below average (redder in color), some areas, especially in the southcentral part of PA, experienced significantly wetter conditions (more green in color).

Figure 2. Source: The Northeast Regional Climate Center   

Field Production

Downy mildew on jack-o-lantern pumpkin is now being reported in three counties across Virginia, a couple in North Carolina, and one in northwestern Ohio. It is being reported on butternut squash in Massachusetts and eastern Tennessee. All other nearby reports have been on cucumber and cantaloupe. Powdery mildew continues to be reported on a wide array of cucurbit crops in both the greenhouse and field, which is typical for this time of the season. On pumpkin and other decorative cucurbits, as the fruit mature, it is essential to continue to protect the handles with a fungicide program until close to harvest to prevent them from becoming brown and shriveled, thus reducing marketability.

Aside from bacterial leaf spot and Phytophthora blight, anthracnose is one of the most common diseases on pepper. It starts as small depressions in the fruit that enlarge and become covered with salmon to orange-colored spores. Pepper fruit are susceptible at any growth stage compared to tomato fruit which are primarily susceptible at later stages of maturity. The same pathogen can also cause anthracnose on strawberries commonly grown in diversified vegetable production systems. Host resistance is not available, so fungicides are the primary tool, especially in fields with a known history of the disease. See the 2022-23 Mid-Atlantic Vegetable Production Recommendations for a list of recommended in-season products. Roguing symptomatic plants and maintaining a three- to four-year crop rotation out of susceptible hosts can help reduce inoculum pressure.

The summer tomato diseases, early blight, and Septoria leaf spot continue to be reported, and this past week gray leaf spot or Stemphylium leaf spot caused by several species of Stemphylium was confirmed. Symptoms can be easily confused with early blight and Septoria leaf spot; however, the lesions will not develop concentric rings characteristic of early blight and will not have the small dark spots (pycnidia) in the center of the tan lesions as with Septoria leaf spot. The lesions will be small and tan in color and commonly crack in the center. It is most common on heirloom tomato cultivars that lack resistance compared to hybrid tomato cultivars. Recommendations for managing early blight and Septoria also apply to gray leaf spot. Bacterial spot and bacterial canker on tomato continue to be confirmed in various regions of the state.

Figure 3. Tan lesions characteristic of gray leaf spot on the upper tomato leaflet, compared to Septoria leaf spot on the bottom leaflet. Photo: Meg McGrath, Cornell University

On the insect front, we continued to see cabbage looper active in cabbage, kale, and other cole crops, and spotted and striped cucumber beetles are still being reported in cucurbit fields. Be on the lookout for wireworm damage in potatoes. This pest leaves scars or tunneling on developing tubers, increasing the risk of soft rots. Although damage can occur now, management must be done before planting. Foliar insecticides do not control wireworms since their feeding is belowground. Adults lay eggs in grassy areas, so managing weeds and avoiding planting potatoes after a grass hay crop can help reduce risk. Larvae are long-lived for up to six years, so long-term rotation away from potatoes is essential. Tillage or insecticides applied at or prior to planting can also be used.

We have begun to see Allium leafminer activity in cooler Pennsylvania regions. The fall generation of this pest emerges as nights cool down for the season and can last 5-7 weeks. Row covers can help prevent damage to any susceptible crops if applied before the emergence of adult flies. If not using row covers, scout for their activity by looking for rows of small white dots near the highest point on leaves (Figure 4) and consider applying a systemic insecticide along with a spreader-sticker surfactant during the period of adult flight and shortly after to control larval feeding.

Figure 4. Oviposition marks by Allium leafminer will appear as a row of small white dots along a leaf, often near the tip or at the highest point on a bent leaf. Photo: Karly Regan, Penn State

Berry Crops

Leaf diseases are being seen in some plantings of brambles. These include primarily raspberry leaf spot, which, as the name implies, is common on raspberry, and Septoria leaf spot, which affects blackberry, though anthracnose can cause leaf spots as well. These diseases look very similar in appearance. The first two can cause defoliation mainly of lower leaves if they become severe enough, affecting plant vigor and ability to make carbohydrates going into the fall. The usual cultural practices such as removing old fruiting canes, keeping rows narrow, controlling weeds, and trellising plants to improve airflow will help.

Figure 5. Raspberry leaf spot on black raspberry (left). Photo: Karly Regan, Penn State. Septoria leaf spot on blackberry (right). Photo: Kathy Demchak, Penn State.

This is also the time of year when late leaf rust can become a problem on red or black primocane-fruiting raspberries. This disease is not a systemic rust (like orange rust is), so there is no need to pull the plants out. For all the above diseases, certain fungicides in categories 3 and 11 (check labels to see which ones list the above diseases) are helpful in control.

Spotted wing drosophila is continuing to be problematic. Anyone with day-neutral strawberries should keep an eye peeled for soft spots on the fruit, and growers of berries should watch for a noticeably shorter shelf-life. Employ all the cultural controls you can (thorough harvests, reduced intervals between harvests, and refrigeration) and use insecticides as needed.

Figure 6. (Left) Late leaf rust on 'Niwot' black raspberry. (Right) Powdery mildew on 'Galletta' strawberry. Photos: K. Demchak, Penn State

Fall is when powdery mildew can take off in strawberries. Watch for inward leaf curling and purple blotches that first show up along the leaf edges. Day-neutral cultivars are especially susceptible, as is the June-bearing cultivar Galletta. Fungicides are generally unnecessary unless the disease is severe or the fruit is affected. Fungicides that specifically list powdery mildew on the label (category 3, 11, or specific fungicides such as Quintec) are effective, but fungicides used for other common diseases such as gray mold have little effect.