Strawberry IPM Newsletter No. 4 – June 10, 2016
Click on photos to enlarge.
Spider Mite and Tarnished Plant Bug Numbers Climb
Southern Fields Nearing Harvest
Some much-needed rain this week should help size-up berries that are nearing harvest in southern Maine. Hail, however, was an unwanted addition to some storms and has caused some significant localized crop damage. Northern fields still have late varieties in bloom, and may still need protection against tarnished plant bug and gray mold infection. A few fruit are being harvested for stands from plasticulture plantings and fields put under row covers this spring.
Strawberry bud weevil or “clipper”
Most fields in Southern Maine are now beyond early bloom stage when clipper can have an economic impact. If your fields still have late varieties in early bloom, you should continue scouting for clipper and apply controls if significant damage is noted to the buds. Be aware the clippers will move on to raspberries and blackberries and clip off their buds once the strawberries have come into bloom.
Tarnished plant bug activity has been increasing in southern Maine this week, with two sites over the recommended spray threshold. More northern sites are still seeing very little if any, activity. Continue to scout for the small, green nymphs until the primary (king) berries begin to color. Remember, these can build up fast. The threshold for nymphs is 4 or more flower clusters infested per 30 clusters sampled. Insecticide options for tarnished plant bug include malathion, Assail®, Brigade®, Bifenture®, Danitol®, and PyGanic®. Thionex® is also labeled on strawberries for tarnished plant bug and spider mites, but this registration will soon expire. All supplies must be used up by July 31, 2016.
Two-spotted spider mites continue to be the most widespread concern this week, with mites being found in nearly every field, and over the recommended spray threshold at three locations. Mites can build up very rapidly under warm, dry conditions. If 25% of leaves sampled (e.g. 15 out of 60) have any mites, a spray should be applied.
Diseases: Many fields are getting ready for a second or third application of fungicide to prevent gray mold, in anticipation of weekend rains, which could result in more fungal spores being released to infect remaining flowers. Two to three sprays of fungicide through the bloom period are typically required to provide good protection.
Anthracnose fruit rot could be a threat when fields are wet during fruit development, especially under warmer temperatures, such as is often seen with plants grown on black plastic mulch. It may be best to use a fungicide product that offers control of both gray mold and anthracnose, such as Pristine® or Cabrio®.
Leather rot (Phytopthora cactorum) could also appear in fields if standing water is prevalent for an extended time following heavy rains or overhead irrigation. Aliette®, Agri-Phos® or Phostrol® applied during fruit development can help prevent leather rot when the risk of this disease is high. Fungicides typically used for gray mold are generally not effective on anthracnose.
David T. Handley, Vegetable and Small Fruit Specialist
P.O. Box 179
Monmouth, ME 04259
491 College Ave.
Orono, ME 04473
Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture Cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment. A Member of the University of Maine System.
Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.