In the Orchard Starting the Season

Spring 2011

European apple sawfly larva damage
European apple sawfly larva damage. Photo by C.J. Walke

By C.J. Walke

As winter draws to a close, the days continue to lengthen and we approach early March, it is time to prune the orchard (see The MOF&G, Dec. 2010-Feb. 2011), collect scionwood for grafting, prepare to plant young trees and patiently await the brilliant bloom of the orchard, marking spring’s arrival. This article focuses on reducing overwintered fungal inoculum, applying sprays that awaken orchard biology and boost tree health, and preparing for two insect pests that emerge around bloom time, ready to attack young fruitlets and planning to mass reproduce in your orchard.

Neem Oil and Liquid Fish – Boosting Biology

In the MOFGA orchards, I spray neem oil and hydrolized fish four times in early spring to help awaken orchard biology. Northern New Hampshire orchardist Michael Phillips calls this “stirring the biological stew.” (For greater detail see Phillips’ book The Apple Grower.) Neem oil, pressed from seeds of the Indian tree Azadirachta indica, has three significant compounds that benefit orchards: azadirachtin disrupts insect pupation and feeding; terpenoids help boost a tree’s immune functions; and fatty acids feed beneficial fungi in the soil and among tree roots. Hydrolized fish, commonly referred to as “liquid fish,” provides a nitrogen boost and contains fatty acids for beneficial fungi. Note that cold-pressed neem and hydrolized fish are not heat-treated, while fish emulsion and most neem derivatives are. That heat kills most of the biology in those products.

I make these four applications when apple trees are at half-inch green, at pink, at petal fall and at roughly 10 days after petal fall, mixing 3/4 fluid ounce of neem and 1 fluid ounce of liquid fish per gallon of water (both mixed into the same gallon of water). For the first spray at half-inch green, I cover the entire branch structure of the tree, as well as the trunk, the ground within the drip line, and any collections of leaves that have not yet decomposed. The following three applications are focused just on the tree. These spray applications are intended to reduce overwintering scab inoculum (see The MOF&G, Sept.-Nov. 2010); disrupt insect pupation to prevent larvae from reaching maturity; and stimulate orchard biology and beneficial fungi. Most importantly, I do not apply these materials during bloom, because the oils can kill blossoms and harm beneficial pollinators.

European Apple Sawfly and Plum Curculio

These two pests are common in the Northeast and are very likely to be present in an established orchard. European apple sawfly overwinters a couple of inches below the soil line, emerges as an adult at apple bloom, lays eggs at the base of flowers, and then the hatched larvae eat into apple fruitlets. The characteristic sign of sawfly damage is a winding scar on the surface of the apple, made by larvae in the first instar stage. The damage is often found on drops and sometimes on harvested fruit. Surround (a kaolin clay product) can be applied at pink to discourage egg laying, but sticky white cards hung before bloom will mimic flower color and trap adults, which may be more practical for backyard orchards.

Plum curculio overwinters as adults in ground litter or in the soil, emerges during bloom, makes crescent slits on fruitlets to lay eggs, and then the hatched larvae eat into the fruit. Long considered the “Achilles heel” of organic orcharding, plum curculio can be managed successfully with the push-pull strategy of Surround and a trap tree. Apply Surround right at petal fall to both apples and plums, and reapply it about once a week until pressures subside. For the trap tree, choose an early bloomer with fruit that you are willing to sacrifice, and leave it unsprayed. The Surround should “push” the curculios away from the protected trees and “pull” them to the trap (unprotected) tree. Cover the ground under the trap tree with a tarp, carpet scraps or something else that will prevent curculio larvae from reaching the soil, which is what they will try to do in order to pupate. Then every few days, collect the larva-infected fruits that fall from the tree and put them in the trash or feed them to livestock. Do not compost or dump these fruits on the ground – the larva will survive!

Keeping a clean orchard is the most effective insect and disease strategy for those with backyard or small orchards who may not be equipped for or interested in applying sprays. Collect all drops a few times a week, especially in late-June through early-July, and dispose of them properly. If you do use a spray, please remember to carefully follow all instructions printed on material labels and to use any required personal protection equipment.

C.J. Walke is MOFGA’s development associate, librarian and organic orchardist. You can address your orcharding questions to him at 568-4142 or [email protected].

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