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Degree Days

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Volume 61 Number 9 Date 06/23/2016


POTATO LEAFHOPPER - This insect is appearing in greater numbers in orchards as harvesting of second-crop hay increases. Non-bearing, one- to two-year-old trees are most susceptible to leafhopper feeding and should be monitored for upwards leaf cupping and yellowing of terminal shoots caused by the adults and nymphs. Treatment is justified at levels of one or more nymphs per leaf when symptoms are apparent.

SPOTTED TENTIFORM LEAFMINER - Moths of the second flight are emerging in substantial numbers, with pheromone trap counts ranging as high as 1,209 per trap and averaging 279 per trap. Peak moth activity should occur by early July across southern and central Wisconsin and a week or two later in the southeastern, east-central and northern areas. Apple orchards with populations greater than one mine per leaf or a history of STLM damage are candidates for control of second-generation leafminer larvae.

REDBANDED LEAFROLLER - The orchards in Dane, Grant, Iowa, Kenosha, Racine and Walworth counties reported captures of 50-156 moths this week, indicating the second flight is gaining momentum. Counts of this pest have been very low since the first flight subsided in early June, but are expected to increase markedly during the first week of July.

APPLE MAGGOT - Emergence of the first flies of the season could start by June 25 or 26. Initial apple maggot treatments should begin 7-10 days after the first fly appears on a yellow sticky trap and immediately if the fly is found on a red sphere, with later sprays following at 10- to 14-day intervals as long as flies are appearing on traps. A trapping density of 6-12 unenhanced red spheres per acre placed on the perimeter row is suggested. For traps enhanced with an AM attractant, the density can be reduced to one trap every 20 trees on the outside border. Orchards with a history of severe AM problems should also place a few traps in the orchard interior. The economic threshold for apple maggot control is one fly per unenhanced trap per week or five flies per enhanced trap per week.

CODLING MOTH - The spring flight has peaked in most orchards, though counts remain high at some sites. Signs of fruit damage are becoming apparent. Economic counts of five or more moths per trap per week were registered at 15 of 25 locations (60%) during the June 16-22 monitoring period. Apple growers are advised to continue monitoring degree days and CM trap captures until 650-700 units (base 50°F) have accumulated from the spring biofix to determine if additional flights require treatment. Most flights should occur by 700 degree days.

GRAPE PHYLLOXERA - Grape growers concerned about the appearance of phylloxera galls on grape foliage are reminded that insecticide treatments should have been applied at the first sign of gall formation earlier this month. No insecticide can reduce or eliminate the galls once they have formed on the leaves.

SAN JOSE SCALE - Crawlers are emerging from beneath scales in southern Wisconsin orchards. Known "hotspots," or areas of suspected high SJS pressure, can be monitored using black electrical tape on scaffold branches. The tape should be wrapped adhesive side-down, and a thin layer of petroleum jelly applied to the outer side of the tape. Captures of 10-15 crawlers on several taped branches over the course of a few days, or 10 crawlers on one tape with zero on all other tapes, may warrant application. Treatments should be applied once the yellow crawlers are active, but before their white, waxy coverings (white cap stage) start to form on the leaves and branches. Conventional products for summer control include Esteem (pyriproxyfen) or Movento (spirotetramat). Options for organic growers are summer oil and biological control.

JAPANESE BEETLE - Adults are emerging in southern and western Wisconsin and neonicotinoids or Neem oil repellant sprays must be applied soon, while populations are low and the beetles are still immigrating into the orchard. Neem oil is appropriate for organic systems and effective when applied repeatedly. PyGanic is another organically acceptable method for immediate contact control, but the material dissipates quickly if applied during the day. A third option is Surround WP (kaolin clay) which deters both Japanese beetle and apple maggots, although its efficacy against Japanese beetle is inconsistent.

DOGWOOD BORER - Pheromone traps can be placed now to provide information on the size and timing of the moth flight, as well as the subsequent larval hatch expected in July.

-- Krista Hamilton, DATCP Entomologist