Mite Management: Reduced Risk Pest Management in Apple

Phytoseid mites (T.pyri) feeding on ERM

Phytoseid mites (T.pyri) feeding on ERM

European red mite have been sporatic in orchards this season with apple rust mite (ARM) beginning to cause ‘silvering’ of foliage in some Hudson Valley orchards. The rust mite are beneficial in small numbers as a food source for predatory mite early in the season. T. pyri (Galendromus =Typhlodromus pyri), Amblyseius fallacis and Zetzellia mali are our three primary mite predators found throughout northeastern orchards. Conservation of mite predators should be considered during the latter part of the season to reduce mite flare-up.

More recently the generalist predatory mite Anystis baccarum (Linnaeus), a large, red, very mobile mite has been found in a western Vermont orchard (Barny and Chris Hodges). Anystis baccarum (L.) [=Anystis agilis (Banks)] (Acari: Anystidae) is a common predatory mite recently identified in apple orchards and in vineyards in Québec, Canada. The mite is in a group of beneficial predator mite species known as velvet mite, sometimes seen throughout the northern regions of north America. It is considerably larger then its prey, the European red mite, Panonychus ulmi (Koch), yet can be misidentifying due to it presence on tree fruit foliage and its red color. This can result in unnecessary miticide applications.

In a recent study to elucidate the residual toxicity of eight insecticides to Anystis baccarum, residues of lambda-cyhalothrin, phosmet, and carbaryl were highly toxic in 48-h petri dish bioassays, however, methoxyfenozide, acetamiprid, thiamethoxam, imidacloprid, and spinosad, were evaluated and found to be nontoxic.

In years where temperatures exceed 80F and dry dusty conditions prevail, two spotted spider mite (TSSM) and European red mite (ERM) can build very quickly due to shortened generational time and irritation by dust for 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.(Table for assessing threshold)

Z. Mali feeding on ERM egg.

Z. Mali feeding on ERM egg.

To maintain the usefulness of new reduced risk materials, managing the build-up of resistance in arthropod populations to insecticides and miticides is essential. Reducing the pressure on a population that selects for the survival of resistant individuals is cited as the primary cause of insecticide resistance. This is often the result of employing a single mode of action pesticide for multiple generations over many seasons. The generally accepted method of reducing selection pressure is to treat each generation of a pest with pesticides of different classes of chemistry. Additionally, the use of oil and non-chemical control strategies such as biological control will contribute to reducing the resistance potential in pest populations.

Temperature effects on generational development time of ERM.

Temperature effects on generational development time of ERM.

The recent shift limiting the use of the organophosphate class of insecticides (OP’s) in pome fruit production through legislation, GAP certified market constraints and public perception has prompted fruit producers to use reduced risk pest management tools to control the arthropod pest complex. These include the neonicotinoids such as Actara, Assail, Calypso and Provado; the insect growth regulators (IGR’s) Intrepid and Esteem; the Oxadiazine Avaunt and the spinosyn Delegate. With the advent of reduced risk (RR) pest management programs come insecticides with generally lower levels of toxicity to predacious insects and mite. However, we have observed mite response (flare-ups) through the use of some RR insecticides, and consistently with the use of imidacloprid (Imidacloprid 2F & 4F; Provado, no longer regestered), and Delegate.

In previous studies it has been demonstrated that the phytoseiid mite, G. (=Typhlodromus) pyri, can be introduced and conserved to achieve biological mite control. The use of RR programs provide a more favorable environment to use biological control organisms to obtain phytophagous mite management while reducing the selection pressure placed on miticides alone. Many of the RR miticides are compatible with the preservation of biological control agents.

Toxicity of Insecticides and Miticides to Predatory Phytoseiid Mite

Toxicity of Insecticides and Miticides to Predatory Phytoseiid Mite

From my perspective, the weak link in the biological control of mites is not solely the use of disruptive insecticides. The fungicide mancozeb (Manzate), belonging to the EBDC group, used to manage apple scab (AS) Venturia inaequalis. Each application of Manzate made prior to bloom reduces T. pyri populations by roughly 30%, with post bloom applications imposing significantly greater reductions in numbers of phytoseiid predators. Given the importance of achieving AS control, the resistance of AS to sterile inhibitors in the Northeast, rising costs of new fungicides and reduced efficacy of Captan alone compared to Manzate (mancozeb) / Captan combinations, it is unlikely that most producers can avoid using mancozeb strictly to maintain biological control agents. Thus the requirement of AS management in scab susceptible apple varieties will limit optimum biological control measures in tree fruit if mancozeb is employed. However, in blocks of low AS susceptible varieties such as the use of scab resistant varieties developed by PRI, would reduce the need for mancozeb, reducing the negative impact on the phytoseiids.

In reviewing the many options for mite management one should be aware of the stage of development that is present in the field. If eggs are high in number, the use of materials with ovicidal efficacy should be selected (Esteem, Zeal, Apollo, Savey/Onager and to some extent Acramite); applications against newly emerging mite larvae (Savey, Zeal) or against motile mites (Envidor, Nexter, and AgriMek) should be made at lower than economic threshold levels when recommended by the label. Considering the impact insecticides and miticides can have on the phytoseiid populations may provide increased levels of phytoseiid presence and enhanced biological mite control. In the table below are pest management tools grouped according to their toxicity against the phytoseiid Amblyseius fallacis.

Below is a list of miticides with a brief description of their use, relative to their class or mode of action. At the bottom of the page is included an efficacy chart based on mite species. Keep in mind when choosing a miticide that many of the newer materials are contact materials requiring complete coverage to be effective. A number of agrichemical companies have added to their miticide label a minimum use rate of 100 gallons per acre to aid in improving coverage. For legal (and efficacious) applications to be made this requirement must be met.

Classes of Reduced Risk Miticides

Class 6:
Agri-Mek, Agri-Flex, Abba: (Avermectin) is a natural fermentation product containing a macrocyclic glycoside, used on apples and pears as an acaricide/insecticide. When used as currently recommended, it controls European red mite and pear psylla, and aids in the control of spotted tentiform leafminer. Abamectin is toxic to bees and predator mites on contact, but the foliar residue dissipates quickly, making it essentially non-toxic to these species after a few hours (low bee-poisoning hazard). Excellent activity against European red mite, two spotted spider mite and apple rust mite.

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 (Clofentezine) is a tetrazine compound used as a contact acaricide that acts primarily as an ovicide/larvicide; it is particularly effective against winter eggs of European red mite. Following early season applications, it gives excellent residual control. Its use in apples is restricted to no later than 45 days before harvest, but in pears, cherries, peaches and apricots it may be used up until 21 days before harvest. It is safe to bees (low bee-poisoning hazard), beneficial insects, and predatory mites. It is not an effective adulticide.

Savey/Onager (Hexythiazox) is a carboxamide compound used as a contact and stomach-poison acaricide. It is effective against eggs and larvae of European red mite; it will not kill adults. It is registered for a single application in all pome and stone fruits, and may be used up to 28 days before harvest. It provides excellent residual control, and is safe to bees (low bee-poisoning hazard), beneficial insects, and predatory mites.

Zeal (extoxazole) is 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.

Class 20:
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.

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 21:
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.

Class 23:
*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:

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.