May 1, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 1 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 1st Call Stream: CLICK HERE

Regional update
Across southern Wisconsin and northern Illinois early varieties, e.g., Liberty, Pristine, SnowSweet, Zestar, are at quarter-inch green. Tight cluster was reported at a location near Lake Geneva on Zestar, and Madison on Haralson, Idared, Jonamac, McIntosh and Zestar. Orchards further north, e.g. La Crosse, Twin Cities and Chippewa Falls, are almost at green tip on these early cultivars. Growers in northeastern WI, near Lake Michigan are still at silver tip on early varieties.

Copper and freezing temperatures
A few growers may have applied copper within 12-24 hours of freezing weather conditions late last week. When freezing temperatures occur, wait to apply copper until 24-48 hours after a freeze. Phytotoxicity problems only arise for green tissue exposed at the time of application, so, freezing temperatures shouldn’t cause a problem with subsequent bud-break if trees have not yet reached green-tip. Tank-mixing of mancozeb and copper should be avoided. Copper offers 5-7 days of protection against scab, so there is no need to spray both products for scab protection. Additional information on copper application can be reviewed in the call summaries for the past two weeks.

Lingering effects of cool weather
According to standard guidelines for fungicide wash-off, precipitation of two inches or more will remove all fungicide protection while an inch of rain will only remove about half of the protectant. Be aware that these guidelines do not consider the effect of precipitation intensity on wash-off. Half an inch of hard rain over 30 minutes will likely remove significantly more fungicide than the same volume of rain falling over 12 hours.

Any detrimental effects from low soil temperatures are likely to be site specific as soil temperatures in the root zone are affected by multiple factors such as slope direction, moisture level, vegetation or ambient air temperature. Soil temperatures are expected to rebound as air temperatures rise. Curious growers are advised to take some soil temperature probes in various blocks. This can be achieved with a digital candy or meat thermometer, which typically has a four-inch probe with the sensor located in the tip. They’re fragile compared to the real things, however, so be careful to avoid any rocks.

Zinc and boron reminder
As a reminder, boron and zinc should be applied either pre-bloom or after petal fall. If concerned about zinc deficiency, apply zinc at pink. Do not apply more than 0.5 lb. of boron per acre per year to avoid boron toxicity and do not tank mix Solubor with oil. For zinc, a foliar application of a common 9% zinc chelate solution (Zn-EDTA) at one quart of Zn-EDTA per 100 gal is recommended. The impact on flower development due to zinc deficiency may explain the phenomena some growers are experiencing where a large “snowball bloom”, e.g., Zestar, is followed by poor fruit set, which may be due to poor germ-tube development.

See page 6 for additional guidance on maintenance and corrective fertilizer programs,

Sprayer calibration
Calibration remains a critical way to ensure we are delivering the correct dose of pesticide across a variety of production systems within an orchard. Variability in row widths, tree size and canopy density, can greatly influence application rates and spray performance. Calibration usually takes about 1-3 hours of work, and evaluates important travel speed, nozzle output, row width and sprayer pressure. Additionally, water-sensitive cards can be hung in trees to show spray coverage, Coverage should be reevaluated after a month.

Spray distribution and coverage
Of most concern is how variability in row widths influences application rates. This is because we are spraying linear acreage vs. square acres in a field. For example, a 20-acre field with a 25 ft buffer on all four sides required for turning around equipment and access to orchard only has 17.8 acres of trees. These 17.8 acres could be further refined to linear acres, e.g., the row width x the row length. This is our actual acres being sprayed and is most likely to be less than what is published on a USDA map.

Filling up a tank and noting where in the orchard it empties out is only a ball-park estimate for your gallon per acre application of water. This tells us nothing about individual nozzle performance, e.g., gallon per minute flow rates. Generally, there is always a bit of spray water left, which can be significant on a 400-gallon tank and if tanks are filled up to their collar, there is likely more water in the tank than its designated capacity, i.e., the tank is over filled when you fill it all the way to the collar.

Image credit:
Image credit:

How we distribute spray across the canopy is determined by the tree canopy or shape. Our nozzles and flow rates we select are what determine where the spray goes on the tree. Filling up the tank and measuring the distance until it is emptied does not tell us if the pesticide landed on its target. Where a tower sprayer is used or on tall spindle trees, spray can be evenly distributed through the canopy. On traditional semi-dwarf trees, spray distribution is skewed towards having 50 – 65% of the spray in the top 2/3 of nozzles.

For more information, check out

Pre-calibration inspection

  1. Make sure sprayer is triple rinsed and filled with clean water.
  2. Clean all screens, nozzles and lines in the sprayer.
  3. Make sure your pressure gauge works. This may require you to take the pressure gauge to a machine shop, implement dealer, welding supply, etc. and have it tested prior to calibration.

Orchards near agronomic crops should consider registering their farms with DriftWatch – an online registry which allows specialty crop producers, apiarists, and pesticide applicators to communicate locations of crops with high sensitivity to pesticide drift, e.g., apples and grapes. This could be especially timely for some, since planting of glyphosate- and dicamba-tolerant soybeans are on the rise. Farmers intending to apply dicamba herbicides on dicamba-tolerant soybeans are required by the pesticide registrant to attend a training and must have proof of completing this training. For more information visit,

Apple scab preparation
This week’s predicted weather, particularly in orchards experiencing several nights of 50°F lows, will rapidly advance leaf development (tree phenology), apple scab maturity and if rain occurs, ascospore release. The combination of rain, wind and warm weather allows a large number of apple scab spores to be released in conditions where trees are pushing out lots of vulnerable green tissue and wind conditions are preventing fungicide treatment. Western and northeastern Wisconsin won’t experience the warm weather rolling through southern Wisconsin where one or more apple scab infection periods may occur.

Prior fungicide applications will be most effective during the first precipitation when all the ascospores that have matured to that date are released. For future reference (scab detective work), it could be helpful torecord the date and time-of-day of your first precipitation this week. While subsequent ascospore maturity development may be rapid given projected temperatures, if we experience multiple rain events this week, these ascospores should be getting released gradually rather than in a single large shower.

During the day, ascospore discharge usually begins within 30 minutes after the start of the rain and is largely completed within 3 to 6 hours. Sufficient fungicide residue needs to be present during this period to prevent an infection, reapplication may be necessary if more than two inches of rain occurred since last application. Performance during this scenario is dependent on coverage, application rate, rainfall, and new leaf tissue since last application. The EBDCs and captan will both experience redistribution during periods of high moisture. To assess wash-off, it is important to monitor rainfall, and relative humidity. A small amount of rain can be enough to generate spore release and high relative humidity can result in long infection periods. Leaves tend to dry very slowly under these conditions.

Lesions from an infection period won’t become visible for at least 10-14 days. One option available to organic and conventional growers is to apply liquid-lime sulfur (LLS) within 72 hours of infection period to burn out early infections. Conventional producers have used a variety of fungicides to burn out scab, however, this practice is not advised due the resistance concerns for DMI, SDHI and QoI fungicides. Avoid applying LLS if temperatures exceed 80°F or within 14 days of an oil application. Liquid-lime sulfur is incompatible with many other pesticides, especially oils and other emulsified materials. Liquid-lime sulfur can induce a thinning response when applied during bloom, so caution is advised when making an application during this time. Do not mix copper or sulfur with biologicals like Serenade (Bacillus subtilis), as both are general biocides.

Weed management reminders
Growers still sitting at silver tip have an opportunity to catch up on orchard-floor management before the weekend. Research has shown that the critical weed-free period in orchards is from bloom through about mid-July, when tree growth and nutrient needs are greatest. Goals for under-tree vegetation maintenance for organic and conventional growers should include:

  1. Excellent weed control from pre-bloom through July;
  2. Maintenance or increase of soil organic matter levels (optimum is 3-6%);
  3. Control of perennial, especially woody, weed species;
  4. Maintenance of under-tree groundcovers, when allowed, to maximize trunk exposure and reduce vole habitat.

In addition to a reduction in fruit size and overall yield, weeds in the tree row can stunt tree growth, especially during orchard establishment. The optimal area for weed management around trees is determined by soil type, tree age, and irrigation availability. In dwarf and semi-dwarf plantings, weeds should be controlled out to two to four feet from the tree trunks in all directions. Smaller weed-free areas may be sufficient in orchards with irrigation or very fertile soils.

On the organic side, weed management is often cited as one of the main challenges in organic production due to the high cost of machinery and materials, and the labor-intensive practices that are often required. Under the National Organic Program (Regulation §205.206(c)), weed problems may be controlled through:

  • Mulching with fully biodegradable materials, e.g., wood chips at 4-6” depth
  • Mowing
  • Livestock grazing. Check for compliance concerns if farm is third-party certified for USDA Good Agricultural Practices (GAP) or similar Global Food Safety Initiative recognized food safety scheme, e.g., GLOBAL G.A.P., PrimusGFS.
  • Hand weeding and mechanical cultivation, e.g., need to operate at 3-4” depths to kill weed crowns, will also cut some tree roots at this depth
  • Flame, heat, or electrical means; or
  • Plastic or other synthetic mulches (must be removed from the field at the end of the growing or harvest season)
    The following link provides a detailed summary of non-chemical weed management methods that can be implemented by all growers.

Organic resources for weed management

Herbicide Reminders

  • Most pre-emergent herbicides require bare soil at time of application. If a significant amount of debris is under the tree, fail mowing or sweeping may be required. If weeds have already began to emerge, adding a post-emergent herbicide may be required.
  • Check the labels. Even though Chateau (flumioxazin) has a 60-day PHI, the label indicates it must be applied before pink bud in apples, whereas Prowl H2O (pendimethalin) only has a 60-day PHI.
  • It is too late to apply some herbicides such as simazine that have 150-day PHI.
  • Consider application timing. Most pre-emergent herbicides required light tillage or rainfall or irrigation to activate and incorporate the herbicide into the soil. Since cultivation is not likely an option, see if your pre-emergent should be applied a few days before light rain showers are forecasted or consider activating your irrigation system to incorporate the herbicide.

Pesticide container disposal