by Tamara Scully
Whether you are growing apples with conventional sprays or organically, the same pests and diseases, and sometimes the same control products, are going to factor into your management program. Either way, integrated pest management can play a major role by ensuring that you are properly treating the crop — using the right practice at the right time — to reduce pest pressures, and to avoid unnecessary labor and expenses associated with unneeded treatments.
Organic tree fruit pest management is not just about the materials allowed under National Organic Program standards, C.J. Walke, organic orchard specialist, said, but “how to go about managing some of the major pests we see in tree fruit.”
Walke described the three levels of steps needed to organically manage pests. These steps can be used in conventional production as well, to decrease reliance on chemical crop protectants while increasing efficacy of a spray program.
The first level of management is to prevent or avoid problems, accomplished by cultural practices. These practices include: crop rotation; cover crops; sanitization; and cultivar selection.
Next, mechanical or physical means to reduce pest pressures are used. Row covers, mulch, flame weeding and mowing are all means of excluding pests from the crop.
In tree fruit production, particularly in the Northeast or other humid growing regions, “in most situations, pest levels can get pretty high,” Walke said, and the first two levels of pest management might not be enough control to produce a marketable crop. When the first two levels of management aren’t working, it’s time for applying crop sprays, either those approved for certified organic production, or a more conventional regime. Bt sprays, dormant oil sprays, kaolin clay and spinosid products are often used in both production methods.
Decreasing Pest Pressures
The orchard environment can go a long way in making trees less hospitable to pests. Orchard diversity, gained via the use of buffer strips, field edges, and stone rows where plants which support beneficial insects are allowed to thrive, is recommended. Yarrow, Queen Anne’s lace, sweet cicely and cilantro are some good plants for attracting beneficial and native predatory insects, Walke said. Adding nesting blocks or nesting tubes for osmia bees, and allowing some muddy spots to develop will provide habitat for the beneficial bugs.
A sanitary orchard environment is the next step in maintaining habitat that does not allow bad bugs to thrive. Keeping the orchard floor clean throughout the growing season is important, as insects are often found in dropped fruits and fungi thrive in leaf matter.
About 30 days after bloom, some major pests become an issue. As fruits drop to the ground during June drop, cleaning them up immediately will disrupt the life cycle of many insect pests. Fungal diseases overwinter in leaf debris and soil. Preventing the inoculum from reaching the soil, or from living in debris over winter, will reduce pest concerns. Moving will help the leaves to decompose quickly.
Parasitoid bugs, like the tachinid fly, will often lay eggs on pests, and the larvae will parasitize the host. Tachinid flies are particular good for targeting early season pest concerns of Japanese beetles, helping to reduce populations.
Monitoring of pest levels can be done by utilizing a variety of sticky balls and traps. Degree day tracking helps growers determine when likely pest pressures will be high by calculating the time between different developmental stages of insect pests. While not all insects life cycles have been tracked, using degree days for those that are available allows growers to target spray applications to the precise time when insects are in a vulnerable life cycle stage, enhancing effectiveness of pesticide applications.
There are several methods of calculating degree days. These daily calculations are cumulative. The biofix day is the first day of tracking, and is associated with the first trapping of a given insect, or a certain stage of plant growth, such as bloom time. More information on degree days can be found at http://ipm.ucanr.edu/WEATHER/ddvideos.html .
Pests to Control
The roundheaded apple tree borer is a major pest in the Northeast. The borer lays its eggs at the soil line, where larvae will feed at the cambium layer for several years. They will completely girdle the tree, and can find their way into the roots, where they then bore up into the tree and pupate into the adult form. There is no control available at the adult stage, so eliminating the larvae is the only option. Keeping the tree soil line clean from debris, utilizing screens around the trunks, and digging out larvae with a wire or a knife are possible control methods. The sign of infestation is orange sawdust — which is the borer’s frass — at the soil line.
The European apple sawfly adult form emerges at bloom to lay eggs. Larvae hatch out of the fruitlets, leaving surface scars, and then burrow into the fruit. Damaged fruitlets will fall during June drop. Cleaning these out of the orchard will greatly reduce pest concerns. When hand thinning, damaged fruitlets should be picked off of the tree. Using a white sticky card at bloom can provide an idea of the pest pressure. Using a kaolin clay deterrent at the apple first pink stage can prevent larvae damage, and spinosid products after bloom can help with control.
Plum curculio affects apples and plums, and is a small weevil that lays its eggs in slits it creates in the fruits. Pyramid traps will help estimate pest pressures. Laying a tarp on the ground to collect drops and prevent the larvae from entering the soil is an effective control method. Using trap trees, which are untreated and allow pests to accumulate on them, rather than productive trees, can limit damage in the orchard.
“It’s still a struggle for most people,” Walke said of plum curculio control.
Coddling moth is another serious pest of apple trees. The adults emerge at bloom. Larvae eat fruits, and then pupate in the trunk. Surround will repel adults, while cardboard bands placed around trees can deter larvae from entering the trunk. Tracking of degree days, to know when to apply Bt spray, begins when the first male is scouted. At 245 degree days, the first generation egg hatch will begin, and is when Bt should be applied with two back-to-back applications. Later in the season, at 1260 degree days, the second generation egg hatch will occur. Coddling moth affects apples and pears.
The apple maggot fly emerges later in the season, and the larvae feed in the fruit, causing late summer fruit drop. They will pupate in the soil. Red sticky balls will help track the emergence of apple maggot fly by attracting it to the apple essence the balls emits. Dormant oils can smother eggs early in the season, while Bt can offer control later.
Controlling pests in the orchard doesn’t simply mean applying sprays. In fact, organic growers are required to utilize cultivation practices and mechanical controls prior to resorting to OMRI-listed sprays. Scouting for pests and using traps to determine pest pressures, tracking degree days; and utilizing management practices that make the orchard less attractive to pests, via sanitation and encouragement of predators are all needed for effective organic pest control in the tree fruit orchard.
C.J. Walke presented a workshop,“Orchard Pest Thresholds,” for the Maine Organic Farmers and Gardeners Association (MOFGA) during the recent Maine Agriculture Trades Show, held in Augusta, Maine.
Apples: Pests to manage
by Tamara Scully