Managing Mites in Ontario apple orchards

Mite populations are starting to increase above threshold in some Ontario apple orchards and growers are starting to consider applying miticides. The good news is that apple growers now have several good miticides from a variety of chemistries available to manage mites. Resistance to miticides can develop very quickly. In Ontario apple orchards, widespread resistance to Kelthane was documented in European red mite (ERM) populations in Ontario apple orchards in 1992. Resistance to Apollo has been found in a few (3-4) apple orchards in southern Ontario in the past, however this resistance is not considered to be widespread. Although we have several new options for managing mites, it is still very important that growers use a resistance management strategy to deter the development of resistance in mite populations.

Growers following a resistance management program for mites should use early season oil sprays to reduce mite populations in the spring. Avoid using insecticides such as pyrethroids that are harmful to beneficial mites or disruptive to phytophagous mites in orchards. Research has also suggested that the application of more than 4 sprays of Assail per year may also be disruptive to mite populations. Miticides should only be applied when thresholds have been reached: (see Pub 360: Fruit Production Recommendations for Ontario). Early season oil sprays are recommended to suppress overwintering European red mite and improve the potential for natural enemies to keep pest numbers below damaging levels. Ideally, no more than one miticide should be used each year. If a miticide is needed two years in a row, it is important to use a product from a different chemical family. While many of the new products work exceptionally well, and have been touted as being less prone to the development of resistance-don't take a chance on applying them two years in a row. The economic repercussions of the development of miticide resistance are much greater than the benefits any miticide. Pree et al. (2005) determined that populations of ERM that were highly resistant to Apollo (>2000-fold), also exhibited low level resistance (4.2-fold) to a new miticide Zeal (etoxazole) which is not even registered here in Canada. This research stresses the importance of using miticides responsibly today, to optimize the efficacy of new miticides that will be registered in the future.

Tips on using miticides effectively

• Monitoring is extremely important in ensuring miticides are applied only where necessary, and at the correct timing. Keep in mind that trees under stress may be more susceptible to damage by phytophagous mites and that hot dry conditions can result in pest population explosions. Consequently, controls may be required earlier under these scenarios. Monitoring is also useful in evaluating the efficacy of miticides.
  
• Be aware of the knock down activity of the pesticide and take this into consideration when determining when to spray. Products which have slower activity such as Envidor should be applied slightly earlier than products which have rapid knock down (Pyramite or Acramite). For information on the activity of various different miticides refer to Pub 360: Fruit Production Recommendations for Ontario.
  
• Check the label to ensure which mite species and life stage are targeted by each insecticide. Envidor, Pyramite, and Kelthane are the only miticides that are effective against apple rust mite.
  
• Apply the proper rate. Some miticides (Pyramite and Acramite) have a higher rate for one type of mite, and a lower rate for other species.
  
• The efficacy of all miticides is dependent on good coverage, so apply enough water with the product.

The miticide programs listed below suggest potential timings for the application of new miticides that are registered in apple. Only one miticide should be applied per season, in orchards where populations are above thresholds.

Table 1: Options for managing European Red Mites (ERM) in Ontario apple orchards.

Timing	Program 1	Program 2	Program 3
½ inch green to tight cluster	Superior 70 oil	Superior 70 oil	Superior 70 oil
petal fall or 1st summer spray (where monitoring indicates necessary)	Agri-Mek® (abamectin)	Envidor® (spirodiclofen) or Acramite® (bifenazate)	Agri-Mek® (abamectin)
OR / AND subsequent summer sprays (where monitoring indicates necessary)	Pyramite® (pyridaben)	Pyramite® (pyridaben)	Envidor® (spirodiclofen) or Acramite® (bifenazate)

Do not apply any miticide more than once per season. Envidor also controls apple rust mite. All of the above products will also provide subsequent control of two spotted spider mites (except superior oil), but be sure to check label for the appropriate rate. Envidor has slow activity and results may not be apparent for up to 1 week.

Both of the new miticides (Acramite® and Envidor®) should be applied at the low end of economic thresholds.

Table 2 Options for managing Two-Spotted Spider Mite (TSSM) in Ontario apple orchards.

Timing	Program 1	Program 2
1st summer spray	Agri-mek® (abamectin)	Acramite® (bifenazate) or Envidor® (spirodiclofen)
OR / AND subsequent summer sprays (where monitoring indicates necessary)	Acramite® (bifenazate) or Envidor® (spirodiclofen)	Pyramite® (pyridaben)

Do not apply any miticide more than once per season. Note: Acramite is more efficacious on TSSM than on ERM, and Pyramite is more efficacious on ERM than on TSSM: Be aware of differences in label rates for different mites.

Reference

D.J. Pree, K.J. Whitty and L. Van driel. 2005. Baseline susceptibility and cross resistances of some new acaricides in the European red mite, Panonychus ulmi. Experimental and Applied Acarology.37: 165-171.

Learn more:

• OMAFRA Publication 360, Fruit Production Recommendations
  

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