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Fall Pest Management Strategies

October 31, 2013

Many growers head into the winter under the false pretense that their facilities will be free of pests and diseases when they begin production the following spring.  Unfortunately, this is often not the case. Whether the production facilities have been empty for several weeks or have crops being over-wintered in them, growers are still at risk of harboring certain pests may become problematic early in the growing cycle the following spring. Here are some potentially problematic pests and management strategies to take into consideration this fall.

Aphids can survive through the winter. Additionally, they produce eggs which overwinter on both crops and weeds. In the early spring, aphids often produce winged forms which are capable of moving across the production site which allows new colonies to become established.

Two Spotted Spider Mites
As the temperatures cool down and the day lengths become shorter in the fall, two spotted spider mites enter a hibernation phase called diapause where they often 'sleep' in non-crop areas such as in cracks and crevices around the production site. Once temperatures warm up in the spring, the mites wake up and move to existing or new crops where they resume feeding.   In locations without freezing winter temperatures, two spotted spider mites may remain active throughout the year.  

Western Flower Thrips
Western flower thrips do not have a hibernation phase, but are capable of surviving cold periods in unheated greenhouses, especially during mild winters. Thrips are capable of surviving at freezing and below freezing temperatures. Plant materials and crop residues provides a safe harbor and allows thrips to survive the winter.

Whiteflies also do not have a hibernation phase; however, their eggs are highly tolerant of cold temperatures. As long as green plant materials are present, there is a good chance whiteflies will survive the winter.

Many diseases are capable of surviving the winter months in non-active life stages. Under the right conditions, a few diseases can actively attack plants with cold temperatures; Botrytis can be active with temperatures as low at 34° F. However, diseases generally do not become very problematic until the temperatures are consistently above 50° F.  

Fall Pest Management Strategies

Growers should not go into fall with the presumption that cold winter temperatures will kill any pests and diseases which may be present. Future problems can be lessened or negated altogether if a few management strategies are implemented now.

Roots and Overwintering
When overwintering plants such as perennials, growers should keep in mind that they are essentially overwintering root systems not shoots. Therefore, it is very important to have healthy root systems going into the winter months. Many growers have found it beneficial to apply fungicide drenches on their crops prior to overwintering them.  Consider applying fall drenches  at least 4 to 6 weeks prior to when the soil temperatures fall below 50° F. This will provide better control of the soil pathogens as well as allow adequate time to rebuild damaged root systems prior to overwintering them.

Insect and Mite Control
It is best to have insects and mites under control prior to fall when the temperatures are cool and these pests are less active. Most of the control products, whether biological or chemical, are significantly more effective while the temperatures are warmer and the pests are more active. Some growers will apply insecticidal soaps or horticultural oils in hopes of suffocating any remaining pests to death prior to overwintering their crops.

Similar to insect and mite management, growers should implement strategies to have diseases under control prior to overwintering plants. During warm spells, it is still possible for Botrytis and other pathogens to attack plants during the winter months. Many growers have found it beneficial to apply systemic fungicides on their crops just prior to the onset of extended periods of cold weather conditions to protect them from pathogens if suitable conditions for disease development should arise.

The presence of weeds in crops or around the production facility is not only a concern for future weed pressures, but are also a great reservoir for overwintering insects, mites, fungal pathogens, and plant viruses. Controlling weeds should be  an ongoing task. Remove any weeds present in crops and throughout the production facilities to lessen the incidence of many problems in the spring.

Cleaning and Sanitation
Growers most commonly consider cleaning and sanitation as an aspect of crop production which they implement just prior to starting crops. Fall is one of the most important times to clean and sanitize production sites.  Removing weeds, plant debris, and old growing mix from the production site will remove overwintering and breeding sites which greatly reduces the amount of disease and insect pressures growers face in the early spring. Disinfectants can also be applied in the fall to control algae, bacteria, and fungal pathogens which would likely affect future crop protection.

The best strategies for preventing spring pest problems are to thoroughly clean production facilities in the fall and take the steps mentioned above to improve root health and reduce the presence of insects, mites, and diseases prior to overwintering.

Paul Pilon
Perennial Solutions Consulting

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