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2016 Spider Mites and Dry Hot Weather

Anna Wallis, Tree Fruit and Grape Specialist
Eastern New York Commercial Horticulture

August 11, 2016

Spider Mites and Dry and Hot weather
Greg Loeb, Cornell Entomology
August 9, 2016

August is often the time we see the emergence of spider mite problems in vineyards and this summer it is particularly important to scout for them because we often see more mite problems under dry conditions. There are several contributing factors but temperatures are usually above average when its dry and these higher temperatures lead to more rapid mite development and more generations and potentially higher populations. Also, beneficial mites often are not able to keep up with the population growth of spider mites with hot temperatures. Perhaps an even more important factor is that with drought conditions the vines will shut their stomates during part of the day to help conserve water and this has the result of increasing leaf temperatures due to lack of transpiration and evaporative cooling. Also, the vine stops adding new leaves earlier in the season in drought conditions and this has the effect of concentrating mites on less leaf material. 
There are good reasons to scout your vineyard for spider mites and/or spider mite damage. I reviewed mites in my spring update, but briefly, there are two species of spider mites that attack grapes in the Eastern US, two-spotted spider mite (TSSM) and European red mite (ERM), but ERM typically is the more common. It is important to know the difference between the two species since some miticides are more effective against one than the other. As the name indicates, ERM is reddish in color and lays red eggs. Adult female TSSM tend to have large black spots on the top of the abdomen but this is a pretty variable. TSSM eggs are clear to opaque. TSSM tends to stay on the bottom side of leaves and produces obvious webbing while ERM can be found on either side of the leaf and does not produce much webbing. Both species have the capacity to go through a number of generations during the season. Because of their small size, it is often difficult to know if you have mites. Foliar symptoms (bronzing of leaves) are one clue, although if you have wide spread, obvious symptoms then economic damage may already be occurring. The working threshold for spider mites (TSSM and ERM combined) in our area is 7 to 10 mites per leaf, although this will vary depending on health of the vineyard, crop load, value of the grape, etc. The impact of mite feeding on grapes includes reduced photosynthesis, delayed accumulation of sugars thereby delaying harvest date, and the potential of reduced yield the following season. I suggest sampling at least 50 mid-shoot leaves from both the edge and the interior (25 leaves each) of a vineyard block, examining both sides of the leaf. A hand lens will be necessary to see the mites for most people. Even with a hand lens, it is challenging to count the mites. Thus, we recommend estimating the proportion of leaves infested with one or more mites and use something like 50% infested as a treatment threshold. A leaf is considered infested if it has one or more spider mites. Remember to keep rough track of which species is most common.
There are several chemical options available for mite control in New York and Pennsylvania: Vendex [fenbutatin-oxide], Agri-Mek and several generics [abamectin], Nexter [pyridaben] (not on Long Island), Acramite [bifenazate], JMS Stylet Oil [aliphatic petroleum distillate], Zeal Miticide1 [etoxazole], Onager or Savey [hexythiazox], Danitol [fenpropathrin], Portal [fenproximate] and the newly labeled miticide called Nealta [cyflumetofen]. Read labels carefully. JMS Stylet Oil is not compatible with a number of other products including Captan, Vendex, and sulfur. Also, although Stylet Oil can help with mite problems, it is not likely to provide complete control in problem vineyards. Nexter is very effective against ERM but higher rates should be used for TSSM. Agri-Mek currently has TSSM on the label but not ERM, although in apples both species are on the label. Acramite includes both TSSM and ERM, although it calls for higher rates for ERM. The new label for Zeal miticide 1 includes both ERM and TSSM in NY whereas the old label only had TSSM. You need a 2(ee) recommendation, which is readily available, for use against ERM with older material. Since Zeal miticide 1 affects eggs and immatures, it is advised to apply before populations reach damaging levels to give the material time to work. Similar advice can be applied to Onager, Savey and Portal. Danitol and Brigade (two-spotted only) are broad-spectrum insecticides that also have fairly good miticidal activity. Pyrethroids are hard on beneficial mites, however.

Spider mites are often thought of as a secondary pest. In other words, something must happen in the vineyard that disrupts their natural control by predators, particularly predatory mites, before their populations can increase to damaging levels. Since Danitol and Brigade have miticidal activity they would not be expected to flare spider mites in the short term. However, in the past, spider mites have been quick to develop resistance to frequent use of pyrethoids. This may or may not happen but it is worth keeping in mind. One of the first things to watch out for is initial good suppression of mites followed by a resurgence indicating the spider mites recovered more quickly than the predatory mites. The other miticides (Vendex, Onager, Savey, Zeal, Acramite, Nealta, and Nexter) are generally pretty easy on natural enemies, although at high rates Nexter can negatively affect predatory mites. Overall, paying attention to conserving predatory mites can pay economic dividends since miticides are quite expensive.

In summary, given how dry things are its worth getting out in the vineyard and scouting for mites and mite damage. While you are out there, also scout for grape berry moth and leafhoppers. As of today (August 9, 2016) we are at about 1600 DD using the grape berry moth phenology model (in Geneva, NY) at the NEWA web site (http://newa.cornell.edu/), so its about the right timing for the third flight of grape berry moth. As we get closer to harvest, you also will want to be cognizant of multicolored Asian beetle in clusters and Drosophila fruit flies (see my spring review for more information). 
For questions, contact Greg Loeb, Cornell Entomology at gme1@cornell.edu 315-787-2345.






European Red Mite (jpg; 15KB)
  • Adult European red mite on bottom side of leaf


Two Spotted Spider Mite (jpg; 11KB)
  • Two spotted spider mite adult. Photo: Jack Clark, UC Davis


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Upcoming Events

October Last Monday Grant Webinar for Fruit and Vegetable Growers

October 28, 2019
4:00 pm

Are you curious about what grants are available to help your farm business?

To help disseminate information on grants on a consistent basis, ENYCH is offering a "current grants" webinar on the last Monday of every month at 4:00pm

Each month's webinar focuses on 1 grant.  The October webinar topic is TBD but might feature Ag Labor Housing Grants.
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Produce Safety Alliance FSMA Grower Training Course

October 30, 2019
8am - 5pm
Canajoharie, NY

A grower training course developed by the Produce Safety Alliance (PSA) that meets the regulatory requirements of the Food Safety Modernization Act (FSMA) Produce Safety Rule.  At least one person per farm producing more than $25,000 worth of fruits and vegetables must attend this course once.  Participants will receive a certificate of course completion by the Association of Food and Drug Officials. 

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Tarping for Reduced Tillage Workshop

November 2 - November 19, 2019

Are you a vegetable farmer already using tarps? Or are you wondering if and how tarps could work best on your farm?

The Cornell Small Farms Program is excited to announce a series of workshops on tarping for reduced tillage in small-scale vegetable systems, to be held in Maine and New York this fall. The Reduced Tillage (RT) project of the Cornell Small Farms Program supports farmers in adopting scale-appropriate RT practices that can lead to healthy, productive soils and greater profitability. Through the evaluation of novel tools and methods using systems-based field research and on-farm trials, the project helps farmers learn about the approaches that can work for their farm. This work is accomplished in collaboration with the University of Maine, and with support from Northeast SARE.

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Announcements

Resources from CCE ENYCHP!

We are developing new ways to connect with the CCE ENYCHP team this year! We have a Youtube page located at this link. Check out videos on Table Grape Production, Pest Updates and the 20 Minute Ag Manager - in 4 Minutes series

We have a Facebook Page here as well as an Instagram page. We keep these places updated with current projects, events, and other interesting articles and deadlines.

There are also text alerts available. Fruit and vegetable farmers in 17 Eastern NY counties can now receive real time alerts on high risk disease and pest outbreaks texted directly to their cell phone. The Eastern NY Commercial Horticulture program, which is supported by local Cornell Cooperative Extension associations, will now offer text alerts to those that enroll in our program in 2019. 

The text alerts will be reserved for important crop alerts that could impact management decisions immediately. For instance, if there were an outbreak of Late Blight in the area, this would be transmitted to vegetable growers.

Farmers can choose the crop for which they wish to receive updates. Additionally they can request that Ag Business Alerts be sent to them. These alerts might include due dates for crop insurance deadlines, market opportunities etc.

If you have questions, please contact enychp@cornell.edu


Podcasts

Climate Change Adaptations

September 30, 2019
In this episode regional vegetable specialist Elisabeth Hodgdon interviews University of Vermont PHD student Alissa White about a series of interviews with growers in the north east concerning climate change adaptations.

Listeners can access Alissa White’s climate change adaptation survey report and additional information on the project by clicking on the following link:

https://adaptationsurvey.wordpress.com/results/
Alissa’s project was sponsored by a Northeast SARE Graduate Student Grant (GNE17-163).

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