NC State Extension

Control Based on Treatment Windows – Winter

WINTER: DECEMBER THROUGH FEBRUARY

Winter (December through March)

Winter (December through March)

Stages of pests. During the winter months, virtually all pests are dormant.

  • RBM — Mites in buds.
  • EHS — All stages present though the fewest number of males and crawlers. There will be more crawler activity if the winter is warm.
  • BWA — Nymphs.
  • BTA — Eggs.
  • Cinara aphids — Frequently there are active aphids even when temperatures drop into the 20s. However, long periods of frozen soils appear to kill out these aphids probably because the tree is no longer able to take up water.
  • SSM — Typically only eggs are present though during warm winters in warm locations there may be active mites.
  • HRM — Eggs present. In some years mites active. Numbers can slowly increase.
  • Predators — Most predators are not active though during warm winters there may be some adult lady beetles feeding on Cinara aphids.

Advantages to winter treatments. The winter months are a good time to focus on control of BWA. Since BWA is in the nymphal stage and no eggs are present, there are many more materials that will control this pest including horticultural oil, Lorsban, and Provado (imidacloprid). Another advantage is that predators and pollinators will not be affected this time of year. Therefore, treating in the winter should not increase problems with mites or scales. For more information on BWA control see: Focus on balsam woolly adelgid control.

The weather can be both an advantage and a disadvantage when treating in the winter. It is a comfortable time of year to spray as it isn’t hot. Some winters are warm with many sunny days, but there is no guarantee it won’t be snowing. Even with warm days, it is usually below freezing at night, which means that sprayers must be protected from freezing. So winter may work well in some situations and in some years, but it is best to have an alternative plan in case the weather doesn’t cooperate.

Control of aphids is typically good this time of year. The synthetic pyrethroids should work well for BTA control for the upcoming spring though it is probably too early for other materials such as Dimethoate or Lorsban to control twig aphids. Any Cinara aphids that are present will be controlled, but Cinaras will have to be controlled again in the fall in trees to be harvested.

Disadvantages to winter treatments Besides issues with freezing temperatures and sprayers, there are other problems that cold weather presents with pest control. One problem with treating this time of year is that mite control will be variable. The HRM is often active during winter months and therefore may be controlled, but sometimes rust mites still aren’t present. The SSM can be active during warm winters, but is typically found only in the egg stage. Products like Talstar may or may not last long enough on the foliage to kill the mites once they hatch. Miticides with activity against mite eggs such as Envidor probably won’t work as the eggs are not active enough for the chemical to be effective. Therefore if SSM eggs are present and mites will be a problem, it would be better to wait until the spring to treat.

This treatment window is not appropriate for control of either RBM or EHS. There may be some suppression of scales but not enough to give long lasting control.

Materials That Can Be Used in Winter
Pesticides RBM EHS BWA BTA* Cinara** SSM HRM
Bifenthrin products(Talstar, Sniper) None None Excellent Excellent for upcoming spring. Excellent if aphids are active but will need to treat again in fall. Poor. Mites may not be active enough for control. None. Added miticides probably ineffective.
Asana None May be some suppression but not long lasting control. Excellent Excellent for upcoming spring. Excellent if aphids are active but will need to treat again in fall. None. Added miticides probably ineffective. None. Added miticides probably ineffective.
Horticultural oil None May be some suppression but not long lasting control. Excellent if coverage adequate. Good for upcoming spring. May be better control if wait until March. Good if aphids are active but will need to treat again in fall. Unknown. May be better if wait until March. Should work well if mites are active. May work better in March.
Lorsban None None Excellent as long as eggs are not present. May control for upcoming spring. Controls made in March may work better. Good if aphids are active but will need to treat again in fall. Little as mites are not active. None
Provado None None Excellent as long as eggs are not present. Unknown. Probably little. Good if aphids are active but will need to treat again in fall. None None
Safari None Is probably too early to get good control. Excellent None Good if aphids are active but will need to treat again in fall. None None

*BTA control is for that spring. Control will not carry over to the following year.

**Cinara aphid control is for that spring. If trees will be cut in the fall, trees will have to be retreated that time.

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