During recent drought conditions coupled with high temperatures, mite populations have increased in apple and stone fruit throughout the fruit growing regions of the state. The high temps provide mite populations very short generational periods, allowing the pest to rapidly increase on tree fruit.
Over the past week we have seen an increase in browning leaves, often associated with Two-Spotted Spider Mites.
Two-Spotted Spider Mites (TSSM) are spider mites in the family Tetranychidae. They are common arthropd pest species of tree fruit during the mid-late season. This mite tends to reside on weed host plants in tree rows, often moving into the canopy after application of summer herbicide applications and flaring in high numbers to cause damage to foliage.
The body of the adult female and most immature stages is oval-shaped and usually appears light yellow to green with two large dark green spots on either side. All life stages have eight legs except for the larval stage, which has six. Survival and developmental time and reproduction depend on environmental conditions including humidity and host plant, yet high temperature appears to have greatest influence in reproduction and population growth. Females can lay up to 12 eggs per day on the undersides of leaves with one female capable of laying over 100 eggs during her lifetime. Eggs are often found in webbing that the mites produce. Under ideal conditions, the eggs hatch in as few as 3 days with larvae feeding immediately upon hatch.
TSSM pass through two nymphal stages and become adults after as few as 5 days. New adult females will then begin laying eggs from 1 to 3 days after emerging with mating optional. Egg to adult development may take as few as 7 days at 81° F, and about 20 days at 64° F. Generally, spider mites do best under hot, dry conditions, and develop faster on water-stressed plants and in years when dry dusty conditions prevail as irritation from dust will increased oviposition.
Environmental conditions can exacerbate this situation by tree row burn down weed management causing TSSM to migrate up to foliage while insecticide use of Carbaryl, Imidacloprid and Pyrethroids will result in increased egg laying or ‘mite flaring’. In these situations the time it takes for a mite egg to hatch and mature to the adult stage can occur in about one weeks time (see Chart 1).
Thus shortened interval of development, relative to higher average temperature, typically leads to multiple generations and high mite populations that can require season long management. With a greater number of generations during a season, comes the likelihood of increased resistance potential to the miticide management programs you use.
ERM thresholds of 5 mite per leaf in July and 7.5 ERM / leaf in August should be used as management thresholds.
Low number of TSSM can cause extensive feeding damage to leaves (leaf browning and collapse) when compared to the number of European Red Mite (ERM) present on leaves to reduce photosynthesis (leaf browning and yellowing from reduced cellular chlorophyll).
From field observations both TSSM and ERM are present on apple foliage in the Hudson Valley at varying degrees of infestation levels.
Classes of Reduced Risk Miticides & Labels
Class 6: AgriMek
Proclaim (Emamectin benzoate) is similar to Agri-Mek (abamectin), with activity against the Lepidopteran complex, primarily the obliquebanded leafroller leafminer and mite. Residual activity is shorter than AgriMek with motile mite being the primary target stage. The use of a penetrant is required for mite management and complete coverage is required for mite control with higher sprayer volume recommended. Do not use sticker/binder type adjuvants as they may reduce translaminar movement of the active ingredient into the plant.
Class 10: Apollo, Savey & Onager
Zeal (extoxazole) – derived from diphenyloxazoline, this miticide acts as an ovicide and has molt inhibiting activity against immature mite. Zeal is a contact miticide with translaminar movement, performs much like Acramite against twospotted spider mites, but is more effective on European red mite. It acts slowly with results in mortality taking several days. Labeling requires a minimum gallonage of 100 GPA. Zeal is considered by the EPA to be a reduced risk miticide.
Kanemite (acequinocyl) in the quinoline class of insecticides, is as a mitochondrial electron transport inhibitor (METI), blocking cellular respiration. It should also be limited to one application/year. Kanemite provides quick knockdown and long residual control. labeling requires minimum gallonage of 100 GPA. Kanemite is considered by the EPA to be a reduced risk miticide.
Class 21: Nexter & Portal
Nexter (formerly known as Pyramite) (pyridaben) belongs to the pyridazinone class of miticides. Nexter’s mode of action as a mitochondrial electron transport inhibitor (METI) blocks cellular respiration. Conservative resistance management would recommend the use of METI miticides (Nexter, Portal or Kanemite) to be limited to one application/year. Nexter is an effective miticide against European red mites with less activity against the two-spotted spider mite. Nexter is also effective against the apple rust mites. Boron prevents water-soluble bags (WSB) from dissolving. Care must be taken not to add soluble bag packets of Nexter to tank mixes with Boron and also to rinse tanks thoroughly after Boron applications prior to using WSB. Labeling requires a minimum gallonage of 100 GPA.
Portal (fenpyroximate) a phenoxypyrazole class of insecticide, is as a mitochondrial electron transport inhibitor (METI), blocking cellular respiration. It should also be limited to one application/year. Portal acts as a contact miticide, requiring complete coverage. Labels state that the miticide rapidly stops feeding and egg laying with 3-7 day mortality observed in the field. Portal is considered by the EPA to be a reduced risk miticide.
Class 23: Envidor
*Envidor (spirodiclofen) is from a tetronic acid which disrupts the endocrine system, affecting energy production. Envidor is an IGR- insecticide with slow activity compared to quick knock down activity, requiring early intervention. Envidor is not acutely toxic to adults and may affect some insect pests as well as mites. Envidor should not be used with oil. Labeling requires a minimum gallonage of 100 GPA.
Class 25: Nealta
Nealta miticide is a suspension concentrate formulation containing the active ingredient cyflumetofen, a member of the beta-ketonitrile class of chemistry. When used as directed, Nealta provides knockdown and residual control. of tetranychid mites on the crops listed on this label. Nealta is a highly active contact miticide on egg, nymph, and adult stage tetranychid mites (ERM & TSSM). Because Nealta is not systemic and has no translaminar activity, thorough coverage of plant surfaces is necessary for effective control. Nealta is not effective on non-tetranychid mites such as rust mite.
Unknown Mode of Action: Acramite
Acramite (bifenazate)- is a hydrazine compound derived from carboxylic acid ester. Its mode of action is a GABA (gamma-aminobutryric acid) agonist in insects. Acramite has quick knockdown, is primarily used against the motile stages of mite, and has some ovicidal activity. Acramite is a specific, selective miticide, with good activity against spider mites but little to no rust mite activity. Labeling requires a minimum gallonage of 50 GPA. Acramite is considered by the EPA to be a reduced risk miticides.