This mite species overwinters as tiny red eggs around cane nodes. In the spring, mites move to foliage where several generations take place. Populations are highest in mid to late July. Concord is among the most susceptible varieties; among vinifera grapes, Riesling is susceptible. Mites are small, dark red, with hairs protruding from dorsal tubercles. Eggs are laid on undersides of leaves. After egg hatch, the first active stage is the larval stage. The subsequent stages are protonymph, deutonymph, and adult. Toward the end of the deutonymph stage, the female mite becomes quiescent and exudes a pheromone which attracts a male mite. The male hovers close to the female until she emerges as an adult. Mating then takes place. Mated females lay eggs that give rise to females; unmated females lay male eggs. Immature and adult mites feed by piercing leaf epidermal cells and extracting cell contents, causing chlorosis and a bronzing effect. Fruit sugar reductions of up to 1.5% have been recorded in Pennsylvania.
Choice of acaricides is increasingly limited. The following acaricides are registered on grape: Kelthane, Vendex, Pyramite, Pyrellin and Acramite. It is important to rotate materials and not rely on a single acaricide, even if a grower considers it to be the most effective. Repeated consecutive use will hasten the development of resistance. Do not spray for mites preventatively; use an economic threshold of 10 mites per leaf (20 on labrusca types), if more than minor bronzing occurs. Some leaf discoloration should be tolerated; this will allow enough mites to be present to support a population of predators. If this population level is reached, but the leaves look healthy, do not spray but repeat counts soon (at least weekly). Use a hand lens when making mite counts; note the presence of eggs - this will give an idea of the population to come!
Growers with a history of ERM infestation should consider an oil spray in the early spring. Dormant oil sprays (just before ERM egg hatch in mid-April) have been effective in tree fruits. Effectiveness in vineyards will be less because of the rough bark and greater difficulty in covering the eggs with spray solution. If dormant applications are made, use high volume sprays to allow material to run into crevices where egs are laid. Highly refined oils (e.g. Stylet and Ultra-fine oil) have been used successfully in the summer as well. Applications of fine summer oils should be repeated weekly as long as problem populations persist.
Spider mites are induced pests, and may
by protection of arthropod
in the vineyard, especially Stethorus
punctum and Amblyseius
(=Neoseiulus) fallacis. The following pesticides are
or otherwise disruptive to A. fallacis and should be used with
if ERM has been a problem: Insecticides: fenpropathrin
dicofol (Kelthane), methomyl (Lannate), carbaryl (Sevin), Fungicides:
captan, Herbicides: glufosinate (Rely),
(Goal), paraquat (Gramoxone), glysophate (Roundup). A.
overwiners in the ground cover, and some herbicides can impact the
before dispersal into the canopy.