Anna Wallis, Janet van Zoeren and Monique Rivera,
Cornell Cooperative Extension & Cornell University CALS Program

What are the actual regulations? 

Diazinon and Ziram are two materials recently under scrutiny in tree fruit production. Diazinon is an organophosphate insecticide, that has been an effective management tool for pre-bloom control of San Jose Scale and post-bloom for broad spectrum control of major pests. Ziram is a contact carbamate fungicide, that has been used effectively as a summer cover spray for apples, to manage diseases including sooty blotch and fly speck, summer rots (white, black, and bitter), apple scab, and Fabraea leaf spot. 

All pesticides are routinely reviewed by governmental and non-governmental agencies. This happens both on a cyclical basis and in special cases in response to new/changes in available information. During this process, the agencies take into account all potential risks as well as the value (based on label uses) of a product and make a decision whether it meets modern standards for human health and environmental safety. After a re-evaluation is proposed, the agencies accept public comments and revise the proposed decision accordingly. In addition, a phase-out period is created for products and label uses that are eliminated. 

In Canada following this review process, Ziram is no longer permitted for use on agricultural uses (re-evaluation decision doc RVD2018-39). Similarly, Diazinon uses were lost for tree fruit crops in 2009 (RVD2009-18). The phase out period for Ziram was 2 years following the published decision (December 14, 2018), meaning the last date of use was December 14 2020 in Canada. For Diazinon, phase out depended on crop: last use date for apricot, peach, plum, and prune was December 31, 2013; for cherry and apple December 31, 2016. 

As a result of these decisions, existing Maximum Residue Limits (MRLs) were removed for both active ingredients, and therefore reverted to the default MRL of 0.1ppm. Fruit exported to Canada must not exceed this 0.1ppm for either Diazinon or Ziram. 

In the United States, current residue tolerances can be found in the Electronic Code of Federal Regulations. In Canada, Health Canada’s Pest Management Regulatory Agency (PMRA) is responsible for this work and the MRLs are available in the MRL Database. At an international level, the Codex Alimentarius Commission, established by FAO and WHO, sets food standards, guidelines, and codes of practice, including residue tolerances. The goal of these standards is to ensure safety, quality, and fairness for international food trade; they are not however, a replacement for each nation’s legislation. 

What are our Diazinon alternatives if selling to Canadian markets? 

Diazinon is primarily used in NY apple orchards to control San Jose Scale and Woolly Apple Aphid. In truth, if you have a heavy infestation of WAA this summer and are able to apply Diazinon based on your market niche, we would still recommend you do so. However, there are some alternatives available. 

• Step 0.5. Most folks are finishing up pruning at this time, but just a reminder that the more opened up the interior of the canopy is, the less likely for SJS or WAA to build up in your trees. This is in part due to increased spray coverage, but also because SJS and WAA both like protected, humid, shaded environments. Well pruned or 2D tree canopies can still foster pest infestations, but are less likely to. 
• Step 1. Spring oil. A ½” green through early pink oil application (2% oil earlier in the season, 1% oil by pink) will help “clean up” SJS and WAA overwintering populations (note that not oils are not specifically labeled for WAA management, but likely to provide some suppression if applied to target other insects). You could add Esteem (5oz per acre) for added efficacy against SJS. When applying horticultural oils, always remember that oil within 48hrs of a freeze event, OR a Captan or Sulfur application, will likely cause russetting!! 
• Step 2. Summer cover sprays. If you have a history of damaging populations of either of these pests, we’d recommend you control for them at PF/1C timing, even before you begin to see populations build up this year. Then, a second application may be called for ~July/August, if you find a population while scouting. 

When applying products for WAA or SJS, spray coverage is key! Always mix the product in the recommended rate of water, use any recommended adjuvants, and avoid “saving time” via driving too fast or alternate row sprays. If you’re going to apply an insecticide, do it right instead of doing it sloppy. 

Highly effective summer cover spray options for  WAA include Spirotetramat (Movento or Senstar (also includes Pyriproxyfen)). Movento is especially effective during the petal fall through first cover timing, because it takes time to be translocated throughout the tree to achieve maximum efficacy, and it must include a penetrating adjuvant. Later in the summer we recommend you scout for WAA by examining the interior of the canopy, especially where large limbs were pruned out, and on more susceptible cultivars such as Fuji or where you’ve noticed hotspots in the past. If you begin to notice WAAs in July/August, you can apply Burkholderia (Venerate SC) or Flonicamid (Beleaf) to target those aerial colonies; these have moderate efficacy but work more quickly than does Movento or Senstar. Note that neonics Assail (with a NIS) or Admire Pro applications during mid-summer timing will have moderate efficacy against WAA, but I don’t recommend using them solely to target WAA. However, imidacloprid (Admire Pro) can be applied as a soil drench during the cover sprays timing. 

Highly effective summer cover spray options for San Jose Scale include Movento, Senstar, Esteem, and Sivanto Prime. Refined summer oils such as JMS Stylit Oil are also effective, but as mentioned earlier, can cause russeting if used withing 48hrs of a Captan or Sulfur spray. Time sprays using the Degree Day model available on NEWA (https://newa.cornell.edu/san-jose-scale).