Greenhouse — Page 2 — Plant & Pest Advisory

July 10, 2022 Andy Wyenandt

Identifying and controlling leaf mold in high tunnel & greenhouse tomato production

Leaf mold occasionally appears in high tunnel or greenhouse tomato production in New Jersey. However, under ideal conditions the disease will develop in field-grown crops. The fungus will cause infection under prolonged periods leaf wetness and when relative humidity remains above 85%. If relative humidity is below 85% the disease will not occur. Therefore, the proper venting of high tunnels and greenhouses on a regular basis is important. The pathogen can survive (overwinter) as a saprophyte on crop debris or as sclerotia in the soil. Conidia (spores) of the fungus can also survive up to one year in the soil.

Symptoms of leaf mold on infected tomato plant. Note the bright yellow leaves and the olive-green spores developing on the undersides of leaves.

Symptoms of leaf mold on infected tomato plant. Note bright yellow leaves and olive-green spores developing on undersides of leaves.

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Filed Under: Vegetable Crops Tagged With: Greenhouse, high tunnel, leaf mold, tomato, tomato diseases

July 1, 2022 Andy Wyenandt

Identifying white mold in tomato production

White mold, or timber rot, is caused by the soil-borne fungal pathogen, Sclerotinia sclerotiorum.

High tunnel tomato plant with main stem infected by white mold.

The photo on right shows a high tunnel tomato plant with main stem infected by white mold. Over time the entire plant will slowly collapse looking similar to a wilt or root rot pathogen as the water supply is cut off to the plant.

White mold is common and once introduced into a field or high tunnel it can very difficult to control. The pathogen produces black sclerotia on the surface and inside infected stems. Sclerotia, if they make their way back into the soil, can survive for years causing significant problems.

Infected stems will turn a light brown color and dry up becoming brittle. If the main stem is infected the entire plant will collapse looking like a wilt or root rot issue.

Under hot, humid conditions white fungal growth will develop on the surface of the stems and in some cases sclerotia will develop on the outside of the stem. Breaking open the stem will reveal numerous black sclerotia.

All infected plants and or plant material need to be removed immediately and disposed of properly. Preventative protectant fungicide programs beginning at flowering will help control white mold. Cool, wet weather and poor air circulation favors disease development.

There are a number of control options for conventional and organic growers listed in Table E-11 in the 2022/2023 mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Tomato stem infected by white hold. Note the fungal growth on the surface of the stem.

White mold of tomato. Note the black sclerotia developing inside the brittle stems.

Filed Under: Vegetable Crops Tagged With: Greenhouse, high tunnel, tomato, white mold

April 21, 2022 William Errickson

Scouting for Broad Mites in the Greenhouse

Broad mites (Polyphagotarsonemus latus) are an extremely small species of mites that affect many ornamental crops. At this point in the season they may be active in the greenhouse and should be included in all greenhouse IPM scouting programs. Broad mites are only 0.2 mm long, which is about half the size of a two-spotted spider mite. This makes them nearly impossible to spot with the naked eye during regular routine scouting and challenging to locate, even with the use of a hand lens. They have a translucent yellow-green appearance and a short but rapid life cycle ranging from 5 to 13 days.

Broad mites under microscope

Broad mites feed on new growth and emit saliva that is toxic to the plants. This results in leaf curl, stunting, and deformity that may be mistaken for herbicide damage, physiological disorders, or a fungal pathogen. Broad mites tend to favor New Guinea impatiens, Sunpatiens, and dahlia in the greenhouse this time of year, though they may also cause damage to gerbera, ivy, lantana, standard impatiens, snapdragon, verbena, begonia, and zinnia. They can spread via plant-to-plant contact and may even hitchhike on whiteflies or aphids to reach a new destination.

Broad mite damage on Sunpatiens. Notice the stunted growth and leaf curling. Photo: W. Errickson

Control can be achieved using miticides that are labeled specifically for broad mites, as some materials that are effective against two-spotted spider mites and spruce spider mites may not work as well on broad mites. Effective materials include Akari, Avid, Dormant Oil, Judo, Magus, Pylon, SanMite, Sirocco, Summer Oil, and Triact. Always follow the instructions on the label and take note of any sensitivities for use on specific plant species. Rotating chemical classes is also very important when treating broad mites because their rapid life cycle has the potential to lead to the development of resistance in a short period of time. Biological controls involving the release of predatory mites that feed on broad mites have also demonstrated success. Predatory mite species that are effective against broad mites include Amblyseius swirskii, Neoseiulus cucumeris, and N. californicus. Broad mites can be effectively managed in the greenhouse if they are detected early and correctly identified as part of a regular IPM program.

Additional Resources

Broad Mites Fact Sheet, University of Tennessee

https://go.rutgers.edu/zg9kdzod

Broad Mites in Ornamental Crops, Michigan State University

https://go.rutgers.edu/56gic7up

Dealing with Broad Mite, Greenhouse Product News

https://go.rutgers.edu/6doflkwc

Broad Mite is Becoming an Increasing Problem, Greenhouse Management

https://go.rutgers.edu/1pftyvss

Filed Under: Landscape, Nursery, & Turf Tagged With: biological control, broad mites, Greenhouse, IPM, Nursery, ornamentals

May 25, 2021 Andy Wyenandt

Identifying and controlling botrytis in high tunnel and greenhouse tomato production

Botrytis, or gray mold, caused by the fungus, Botrytis cinerea, can cause significant losses in high tunnel and greenhouse tomato production if not controlled properly. The pathogen can rapidly spread during periods when structures are closed and when relative humidity remains high for long periods of time. This often occurs when outside weather remains cool and damp while heating is needed. Gray mold is favored by temperatures from 64° to 75°F and requires only high humidity (not leaf wetness) to become established. The pathogen has a large host range and once established in an enclosed structure it can be very difficult to control (UMASS). The fungus can survive/overwinter as mycelia or sclerotia in plant debris and in organic soil matter (NCSU).