Difficult Strawberry Pests

Silver bullet, quick fix, effective pest management strategy? Unfortunately, none of these phrases apply to the following problems in strawberries: western flower thrips, cyclamen mite, and anthracnose fruit rot. Fortunately these pests are sporadic, and weather-dependent. Although they can cause extreme damage, it doesn't happen every year.

Western flower thrips: Western flower thrips are very tiny insects that can cause big problems in day neutral strawberries. They damage flower parts and developing fruit, causing bronzing and scarred, misshapen fruit (Figure 1). Because thrips hide in flower parts, and pupate in the soil, they avoid contact with insecticides. Because they have multiple generations a year, they develop resistance to insecticides very easily. Control of western flower thrips requires a whole-farm management strategy and lots of help from beneficial insects and mites. Biocontrol programs have been developed for effective thrips management in greenhouses. Research is needed to bring these programs to the field.

Picture of strawberry with western flower thrips

Figure 1

Registered insecticides for thrips suppression on strawberries: Delegate WG. A three to four day re-treatment schedule may be needed if thrips populations are high and increasing rapidly. Maximum 3 applications per year. Resistance to this class of insecticides is a problem in some areas.

Other management strategies for thrips: Encourage naturally occurring beneficial insects by avoiding the use of pyrethroids and other toxic insecticides, especially early in the season. Control weeds, which can support high populations of thrips. Use yellow sticky traps for early indications of a problem.

Research needs for thrips: monitoring techniques, thresholds, using biocontrols such as Orius, and Beauvaria, bee vectoring (use of honeybees or bumblebees to transfer biocontrol agents to the blossoms) , effective products, and sustainable control strategies for day-neutral strawberries.

Cyclamen mites: Cyclamen mite feeding causes wrinkled, distorted leaves (Figure 2), resulting in compact, toughened leaves in the center of the plant. Fruit on infested plants is small, bronzed, with prominent seeds. The first step in cyclamen mite management is to accurately identify the problem, as it is sometimes confused with winter injury , herbicide damage or other problems.

Picture of strawberry plant with cyclamen damage

Figure 2

Mites can be introduced to new fields on infested planting stock. Infestations may first appear in scattered locations. As populations build up, mites move to new plants along the runners or they are transferred from plant to plant by workers or on machinery. Older fields are more likely to have higher populations of cyclamen mite. There are multiple generations each year but populations peak in early spring (bud-green fruit stage) and again in late summer (late August- September).

Registered insecticides for cyclamen mite control: Thionex WSP, Agri-Mek 1.9 EC. There are some use restrictions that interfere with optimum control. Thionex will not be registered after 2016.

Other management strategies for cyclamen mites:

Start new fields with clean plants and avoid planting new fields next to older ones.

Schedule work so activities are done in newer, clean fields first, and older fields last.

Scout fields regularly and carefully rogue out plants with symptoms.

Minimize use of pyrethroid insecticides ( Decis, Ripcord, Matador, etc) which are highly toxic to beneficial mites, can disrupt beneficial insect populations, and lead to outbreaks of cyclamen mite.

Maintain short strawberry cropping cycles, harvesting the field for no more than 2 years if cyclamen mites are a problem.

Introduction of predatory mites, in high numbers, may help keep cyclamen mites in check, but this strategy is experimental. Check with suppliers about the best species of predatory mite to use. Combinations of Neoseiulus fallacis and Neoseiulus californicus have been suggested.

Research needs for cyclamen mite: monitoring protocols and thresholds, effective pesticides, alternatives to pesticides, such as hot water dips, use of biocontrols.

Anthracnose fruit rot: This fungal pathogen can multiply on plants before symptoms show up. When ideal weather occurs, outbreaks of anthracnose fruit rot show up very quickly (Figure 3). The problem is most serious on day-neutrals, because fruit is more likely to be present during the warm, wet weather conditions that favour this disease. Anthracnose is spread from plant to plant by rain splashed spores . It can also spread by workers (and equipment) who pick up spores in one field and move them to another. Fungicides applied during the bloom and green fruit can be used to control anthracnose. The problem is that only a few fungicides are registered to control this disease. Resistance can develop very quickly and is a concern.

Picture of strawberry with anthrocnose fruit rot

Figure 3

Registered fungicides for anthracnose fruit rot control: Pristine, Cabrio. Registered for suppression: Actinovate.

Other management strategies for anthracnose: Use clean plants grown in an accredited program to start new fields. Home-grown plants are more likely to be infected with anthracnose. Use broad-spectrum fungicides in alternation with products registered for anthracnose. Avoid working in fields when they are wet. Avoid working in infested fields and then moving to newer, or uninfected plantings. Instead, schedule work so activities are done in newer, clean fields first.

Research needs for anthracnose: Degree day models to predict infection, information on fungicide resistance in

Ontario, bee vectoring (use of honeybees or bumblebees to transfer biocontrol agents to the blossoms), effective fungicides, and effective use of biofungicides.

For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca