Strawberry IPM Newsletter No. 4 – May 31, 2013
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WARMER TEMPS SPEED STRAWBERRY DEVELOPMENT
Higher Temps also Likely to Increase Insect and Mite Activity
Situation: Damp weather stretched through most of the week again, but now things are heating up fast, and the sudden change of temperature should hasten fruit ripening. High temperatures may also stress plants, especially those that experienced winter injury, grub feeding, or any other factor that compromised the plants’ ability to take up water. If plants appear to be wilting, dull colored or otherwise stressed, it may be necessary to irrigate if soils have become dry, to help stressed plants prosper through the high temperatures. Early varieties in southern Maine are now beyond full bloom, and are showing green fruit. Later varieties are mostly in bloom, and the bees have been active under the better weather conditions. Fields that were under row covers are starting to show a few ripe fruit and more will be ripening fast over the next few days. Insect activity remains pretty low for the time being, although we are starting to see an increase, which will be enhanced by the higher temperatures.
Diseases: The prolonged damp conditions earlier in the week have kept the risk of gray mold infection very high. So, if it has been more than a week since the last fungicide application, or the field has received more than one inch of rain since the last application, it would be best to apply another fungicide spray.
Anthracnose fruit rot is favored by warm temperatures and wet field conditions, a combination many fields will see over the next few days; so consider using a fungicide that will offer control of both gray mold and anthracnose when making your next fungicide application, such as Pristine® or Cabrio®.
Leather rot (Phytopthora cactorum) may also be an issue in fields where standing water has been prevalent this spring. A spray of Aliette®, Agri-Phos® or Phostrol® applied during bloom and fruit development can help prevent leather rot where the risk of this disease is high.
Powdery mildew: We have not yet seen any significant signs of powdery mildew, but we anticipate it may become more evident soon, because this fungus can proliferate rapidly under warm, humid conditions. Some fungicides sprays for gray mold can also offer good control of powdery mildew, including Topsin-M® and Pristine®
Slime mold: I have had a report of slime mold from our friends in New Hampshire this week. Slime mold fungi can occur on strawberry plants and mulch when we get very wet, warm weather in the spring or fall. The mold appears as a creamy white or tan colored, jellylike mass growing out of the soil and up onto leaves and flower clusters or just on top of the mulch. The mass is amorphous and may have gray or black fruiting structures covering its surface. The mold dries out to a hard, crusty structure with powdery spores. Slime mold fungi are not parasitic to plants; they just climb them to improve the spread of their spores, but the masses can smother single leaves or fruits and be unsightly. Slime molds disappear when dry weather returns. They do not require any management.
Strawberry bud weevil or “clipper” is becoming more active as temperatures rise. However, some early blooming varieties have already developed beyond the point where clipper can do significant harm. Most fields had only very light clipper injury in later flowering varieties this week; none of the fields were over the action threshold. Late blooming fields should still be scouted for clipped buds.
Tarnished plant bugs remain fairly scarce this week. We have seen a few adults and some small nymphs in the fields we scouted, but none were over the action threshold. Expect activity to increase as things get drier and warmer.
Two-spotted spider mites were found in higher numbers this week, and distributed over a larger area, but all fields were below the action threshold. The extended cool, wet weather likely slowed spider mite development, but we should anticipate that populations will rise under the recent hotter, drier weather.
Spittlebugs: Be on the lookout for spittlebug masses in your fields as we approach harvest time. Although we haven’t noted any in fields this week, they may start to appear soon. The frothy spittle masses are found on the leaf stems (petioles), just below the leaflets, usually showing up around bloom. Although spittlebugs don’t pose a significant threat to the plants, the frothy spittle masses create an annoyance for pickers. Spittlebugs overwinter as eggs and the nymphs emerge in late May. The spittle masses may be at the base of the plants, so spread the leaves and inspect the crowns, leaf bases, leaf stems, and flower stems looking for them. The small, yellow-orange nymphs will be under the spittle. If the average number of spittle masses is more than two per square foot, a treatment may be warranted. Spittlebugs tend to be a greater problem in weedy fields. Pesticides currently registered for spittlebug control include Provado®, Thionex®, Danitol® and Brigade®.
Slugs may be a problem in some fields this season. Moist conditions encourage the presence of these mollusks. Slugs usually feed at night, leaving large holes and tunnels in ripening fruit. Baits such as Deadline® and Sluggo® offer some control of slugs, but should be used prior to fruit ripening. Pay close attention to label instructions and precautions. Baits should also be applied to the fields in mid-September if slugs have been a problem, to reduce egg-laying.
Highmoor Farm Fruit and Vegetable Growers Field Day July 31, 2013
Plans are well underway for the Highmoor Farm Field Day to be held on Wednesday, July 31. Growers will have an opportunity to tour the fruit and vegetable research plots at the farm, part of the Maine Agricultural and Forest Experiment Station, and hear Extension specialists and guest speakers discuss current research on apples and grapes. University of Maine leaders and state legislators will also be on hand to offer updates on programs and legislation effecting farming in Maine. Please join us for the program, farm tours and lunch. More information will be coming soon.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management
P.O. Box 179 491 College Ave
Monmouth, ME 04259 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.
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