2022 PA Vegetable and Berry Current Issues for September 13

Philadelphia recorded its hottest August on record, with 19 days over 90°F and 11 days of low temperatures above 75°F. Precipitation was highly variable across the state, with the rains over Labor Day weekend alleviating some of the dry conditions from August. Although excited about the rain, many growers are now reporting cracking and fruit rots on tomato and other crops because of the significant rains. NOAA’s Climate Prediction Center monthly temperature outlook forecasts warmer than normal temperatures with there being equal chances of the average precipitation being above or below normal.

Field Production

Celery leaf curl was reported on celery in western PA. It has been several years since there were a number of outbreaks of this disease in PA and other larger celery production regions. It is caused by a couple of species of Colletotrichum and causes the leaves to become curled and distorted, similar to a viral infection or herbicide drift injury. Brownish necrotic lesions will develop near the base of the petioles and on the growing point. The pathogen is suspected to be seedborne, so planting high-quality seed is recommended. Fungicides can help slow the spread, and those in FRAC Group 11 are the most effective. Disease development is favored by wet and very warm conditions (temperatures around 85°F).

Figure 2. Left distortion (left) and petiole lesions characteristic of leaf curl (anthracnose) on celery. Photos: Beth K. Gugino, Penn State

Black rot on brassica crops continues to be reported. Once symptoms develop, management strategies are limited to reducing the spread to other plants through sanitation and copper-based protectant fungicides. Alternaria leaf spot is also still problematic. Some of the more effective fungicides include Priaxor (FRAC group 7 + 11), Switch (9 + 12), Quadris Top (3 +11), and Endura (7). Luna Experience is another option for brassica leafy greens. It is important to check the label for your specific brassica crop.

Figure 3. Severe powdery mildew infection on a pumpkin leaf. Photo: Beth K. Gugino, Penn State

Bacterial spot is showing up on pumpkins close to harvest. The fruit were likely infected much earlier in the season when the bacteria on the leaves were splash-dispersed onto the fruit. The bacteria colonize the fruit's lenticels and other openings, and symptoms will begin to develop once they reach a high enough population. Cucurbit powdery mildew is also running rampant. In fields that are severely infected with powdery mildew, consider dropping back to a protectant program and focus on protecting the handles. There is a greater chance of fungicide resistance developing the larger the pathogen population is that is exposed to the active ingredient. Reports of cucurbit downy mildew are declining, but that does not mean it is not around. As the fruit become more mature, downy mildew becomes less likely to result in reduced yield. It is important to remember that cucurbit downy mildew will not survive once the plant tissue is dead, so it will not survive over winter in the soil and be an inoculum source for the subsequent season.

Rhizoctonia was confirmed on Brussels sprouts. On younger plants, it causes wirestem, which typically leads to plant death as a result of lesions that girdle the stem. It can also cause damping off in emerging seedlings and bottom rot of cabbage. The pathogen has a very complex pathogen population structure so the specific anastomosis group (AG) determines the specific host range, with some broadly affecting lots of different vegetables and others preferring specific types of crops like cole crops. The disease is favored by warm, moist soils as well as high soil nitrogen, which is common after a legume crop or cover crop. In-furrow or directed applications of Moncut or Omega are reported to provide good control, while Quadris, Quadris Top, and Endura provide some control. Short rotations between cole crops can increase potential disease severity because Rhizoctonia is truly soilborne, and inoculum level decreases between seasons without a host.

Figure 4. Lower stem discoloration and girdling as a result of Rhizoctonia infection on young cauliflower plants. Photo: Beth K. Gugino, Penn State

On the insect front, we have seen outbreaks of Harlequin bugs and whiteflies in cabbage, kale, and other cole crops. Both of these insects can be managed with pyrethroid or neonicotinoid insecticides, but applications must be made early. In organic production, pyrethrins may provide some control of Harlequin bugs, while azadirachtin products provide whitefly control. Harlequin bugs are black and orange as both nymphs and adults, and their feeding results in white patches on leaves. Eggs are black and white in color and barrel-shaped, laid in clusters on the underside of leaves. Both pests overwinter in plant residue of the target crop or weedy hosts, so post-harvest sanitation is an important cultural tactic to reduce damage next year.

Pumpkins have continued to host spotted and striped cucumber beetles and aphids. Spider mites have been increasing in greenhouse and tunnel production.

Continue to scout for Allium leafminer by looking for rows of small white dots near the highest point on leaves (pictured below). The fall generation of this pest emerges as nights cool down for the season and can last 5-7 weeks. If not using row covers, 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 5. 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

Spotted wing drosophila on fall-bearing brambles and day-neutral strawberries is a concern right now, and broad-spectrum insecticide sprays for its control will still be needed for at least the next few weeks or until harvest is completed.      

With cooler damp conditions occurring, reports of leaf spots on brambles are continuing to come in, and late leaf rust on red or black raspberries is also being seen.  Fungicides in categories 3 and 11 will help with managing these diseases. This is also the time of year when certain leaf diseases (common leaf spot on mainly June-bearers, powdery mildew on day-neutrals) tend to increase on strawberries.

Figure 6. (left) Phomopsis invading a new blueberry cane. (right) Anthracnose lesions on a black raspberry cane. Photos: Kathy Demchak, Penn State

Botrytis (gray mold) is being seen in field-grown fall-bearing raspberries. Effective products allowed for use on brambles include Switch, Elevate, and Ph-D or Oso with a 0-day PHI and Luna Tranquility with a 1-day PHI. Be sure to rotate chemical classes.

Since several different cane diseases had been seen in blueberries this year, it may be helpful to plan on a fall cleanup application of lime sulfur, applied when the leaves have just fallen from the plants or shortly afterward. Not all lime sulfur products are labeled for this timing and use rates vary with the product, so please consult your chemical dealer for assistance in finding a product that will work for your situation.

Growers of both blueberries and brambles may want to plan on a delayed-dormant lime sulfur application next spring.  Many diseases cause lesions on the canes from which spores are produced in the spring, and lime sulfur will help to decrease the amount of inoculum produced from these lesions.