AppleTalk Blog Post
Friday, April 2, 2021
Contact information: John Aue, Threshold IPM, jgaue@mwt.net
Contact information: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org
Welcome to another season of AppleTalk and thank you for your support and participation. Green tip is expected any day on varieties such as Zestar in southern Wisconsin and northern IL. Even though our first call is not until April 13, there will be an excellent opportunity over the next five days to apply copper and oil. Below you will find a thorough overview of what to consider while planning your first spray of the season. Don’t worry if you are not ready for this, there will be plenty of opportunities over the next two weeks to make this application, but the forecasted highs that are expected to reach 70F across the region make for a particularly good opportunity.
Sprayer calibration
Before we begin discussing the first spray, have you calibrated and tested your sprayer? Follow these six easy steps to ensure spraying success: http://treefruit.wsu.edu/web-article/six-steps-to-calibrate-and-optimize-airblast-sprayers/. If you are not sure how to do this on your own, please contact Peter Werts and he may be able to come out to your farm and show you how it is done.
Preparing for copper and oil at green tip
Copper applied at silver tip or bud-break targets fire blight and apple scab. At this early growth stage and with cool temperatures, bacterial colonies in fire blight cankers are not actively growing. Fire blight cankers become much more active at pink tip and the goal of this early application is to ensure enough copper is applied to persist until early pink through bloom to inhibit bacterial growth.
Note: Once copper products are dry, they are no longer phytotoxic. If there is still enough copper residue remaining at petal fall, this can be redistributed by rainfall on to the developing fruitlets and cause russeting. For the standard copper products on the market, approximately three to four inches of rain between the application and fruit-set will mitigate this risk.
Tips to mitigate risk of phytotoxicity and russeting:
- Apply when drying conditions are good (low humidity).
- Do not apply within 24 hours of a freeze event.
- Eliminate the oil from the application.
- Reduce the rate of copper per acre (but not the total gallons of water per acre).
There are many copper-containing products that can be used for fire blight at bud-break. Formulations may contain copper hydroxide, copper sulfate, copper oxychloride, etc. All formulations function the same way by supplying copper ions, i.e., metallic copper, and it is these copper ions that inhibit bacterial or fungal growth. The hydroxyl or sulphate portion of the molecule does not. When choosing a copper product for fire blight, it is important to compare the amount of metallic copper contained in the different products. This is often represented on the package either as a percentage of dry metallic copper by weight or as pounds per liquid volume.
Another important factor in choosing copper is its longevity, which is dependent on the particle size of the copper salts in the formulated products. The smaller the size, the less likely it is to be dislodged by rain, and theoretically the better the copper will be distributed throughout fire blight cankers. Getting information on particle size for particular copper products can be difficult, however your distributor would likely be able to assist. Some options include:
- Kocide is 30% metallic copper
- C-O-C-S is 50% metallic copper
- Badge contains 2.18 lb. copper per gallon.
For more information visit:
- Demystifying Copper for Disease Management, Brian Lehman and Kari Peter, Penn State, Click Here.
Copper application rates and adjuvants
At bud break, use 1 – 2 lb. of metallic copper per acre and apply with a high volume of water, e.g., 75 – 125 GPA, depending on tree size. A 1% concentration of oil can be used to improve the distribution of the copper within bark and cankers. This helps to distribute the copper to break surface tension. To reduce risk of bud damage, do not apply oil when temperatures have been, or are forecasted to be, below 32°F within 48 hours of the applications. Copper is only a ‘Fair’ rated scab fungicide and will provide about 5-7 days of scab protection.
Track rainfall from the application date, if three plus inches of rain has accumulated by bloom, it’s likely the copper will be gone, and you will need to be more aggressive in controlling bacteria compared to a dryer spring.
Oil applications for early season mite and San Jose scale management
Oil applied between silver tip and bloom will suppress mites and San Jose scale, and delay or avoid the need to apply miticides later in the season. Dormant oils are easiest to work with when temperatures are at least 60 °F or higher. As temperatures increase, overwintering mite and San Jose scale respiration rates increase and the oil application will do a better job at suffocating mite eggs and San Jose scale. There is a very wide range of application rates that may be applied. Most growers apply a 1 – 2% oil and rates as high as 3 – 5% oil is also acceptable. These higher rates may be necessary where scale and mite pressure is most severe. We will discuss mites and scale in greater detail later this spring, but the dormant oil spray is one of the most important opportunities to manage these two pests.
Green tip fungicides
The forecasted temperatures for April and the lack of snow cover through March is conducive to scab development. Scab sprays at green tip should not be delayed, especially if you had scab last year. If you had scab last year, it is recommended to start management in high inoculum blocks earlier, rather than later, since there may be significant ascospore maturity before tight cluster. Delaying green tip fungicides is an option in low inoculum blocks, especially if there is no rain forecasted in the days following green tip.
The amount of ascospore development in terms of pre-bud break is typically small. During spring rains, mature spores could be released (pre-bud break), but would require green tissue to be present for an infection to occur. The bulk of ascospore release will occur between tight cluster and petal fall. Biological fungicides should be avoided until there is significant leaf surface present and temperatures are warmer. Additionally, copper applications may negate the impact of these biological products.
If there is very minimal bud maturation five to seven days after an initial copper application, a mancozeb application may not be needed. Need to look at leaf growth and degree day accumulations (NEWA station) to have a better understanding of the maturation and reproductive rate of the fungi.
Additional notes on copper and mancozeb:
- Do not mix copper and mancozeb. There is no advantage for this.
- The full rate of mancozeb, referred to as the “Pre-bloom schedule†is 6 lb./acre and the half rate or “Extended-spray schedule†is 3 lb./acre and interpreting these two schedules can be confusing. The full rate allows for four six-pound applications where the half rate is seven three-pound applications up to the 77-day pre-harvest Interval (PHI). If the goal is to apply mancozeb past bloom, then it is important to only use 21 pounds maximum for the season and not apply past the 77-day PHI.
