April 24, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, April 24 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

April 24th Call Stream: CLICK HERE

Early season orchard management
Whether growing organically or under IPM, hastening the decomposition of fallen leaves on the orchard floor is an important step toward reducing scab inoculum. While some growers will rake under trees manually, other viable options include flail mowing, machine-raking, sweeping or spraying urea.

Soil moisture assessment
Many growers are concerned about negative ramifications of last week’s abnormally late snow storm hitting a large portion of Wisconsin. Rather than melting snow creating excessive runoff, the majority of the moisture was absorbed by the soil. Every 10 inches of snowfall equals about an inch of water, which equates to about 110 tons of water being added per acre. Considering this large volume of low-temperature water (32-33°F), after-effects on soil temperatures can be reasonably expected. Areas that received substantial snowfall will likely require more solar radiation and take longer for soil temperatures to reach normal spring temperatures.

Data from soil probes indicates soil temperatures are widely uniform across the region. Soils in most of Wisconsin as well as parts of Minnesota and Iowa seem to all fall snugly within a range of (32-36°F). A few curious exceptions include Platteville and Arlington, WI where temperatures are roughly 42-44°F, and Freeport and St. Charles Illinois where the soil reached into the fifties. To investigate further, check out this page on the NOAA website where these soil temperature probe data are displayed.

Tree planting
As soil temperatures recover from the recent snow melt, the lower soil temperatures are of minimal concern for planting trees. Low-soil temperature may have played a role in slowing bud development, but air temperature and photoperiod have greatest influence on plant development.

Soil saturation poses a greater risk during planting and it is recommended to delay planting until the soils dry out. Overly saturated soils at planting time creates an opportunity for Phytophthora to invade newly planted root systems. Phytophthora requires free water in soil to transport spores, and waiting until the ground dries and irrigating young trees as soon as they’re planted or start breaking are advised rather than planting in wet soils. When choosing to delay planting, storage precautions must be followed to limit negative effects:

  1. Upon arrival, open boxes of new trees and the plastic liner to prevent fungal development.
  2. Inspect the quality and condition of the trees right away. Contact the nursery immediately if the trees do not look good.
  3. Roots need to be moist and covered with sawdust, hay or mulch. Do not let the roots dry out.
  4. Store the trees at 34°F in a cooler or cold room with good ventilation. Do not store the trees in a room that is also storing apples or that had apples stored in it immediately before the trees arrived. Ethylene produced by the ripe apples will stress the trees. If apples were stored in the room, it should be thoroughly aired out before storing the trees. The goal is to prevent trees from breaking dormancy while keeping temperatures below 40°F.

Zinc and Boron application rates and timing
Boron and zinc are important micronutrients used to promote flower, leaf and shoot development and improve fruit set and quality. Deficiencies in these nutrients can cause poor shoot and leaf growth. Boron deficient fruit may become deformed and develop corky, dry lesions in the flesh.  For photos visit: https://www.canr.msu.edu/uploads/files/Applenutrition-EricHanson.pdf.

The first application of boron can be applied between late pink and early bloom to promote flower viability and fruit set. This early application will not correct deficiencies identified during routine-tissue analysis. A later application, applied between petal fall and third cover, can be used to correct deficiencies in fruit and vegetative growth. Zinc can also be applied at this time to stimulate early flower bud, leaf and shoot development if tissue analysis shows zinc levels to be deficient.

If tissue analysis from the previous season shows a boron deficiency or deficiency symptoms are observed, boron can be applied once or twice after petal fall. The first application is typically timed for first cover, and the second application is made at third cover. To increase boron, Solubor (20% boron) can be applied as a foliar application (1 lb. per 100 gal) at this time. 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. There’s a very fine line between a boron deficiency and boron toxicity, so be mindful of application rates.

To amend zinc, apply a foliar application of zinc chelate. Most suppliers carry a 9% zinc chelate solution (Zn-EDTA), and recommend using one quart of Zn-EDTA per 100 gal. Zn-EDTA is fairly compatible and if needed can be tank mixed with boron or urea. Always verify label rate before making application.  Applying too high of rate can result in phytotoxicity.

Note: Verify the pH of spray solutions when preparing an application. If the pH of the spray solution is greater than 7, products like Solubor can precipitate out and are no longer effective. It is recommended to not to mix fertilizers with pesticides or oils. Growers concerned about their spray solution pH are recommended to track and record this information on their fertilizer and pesticide records. Add an acidifier if the pH is high. Digital pH meters are an easy and reliable method to verify your spray water pH. The following links highlight how water pH effects the stability of pesticides.

Copper formulations and wash off
Functionally, copper sprays are only able to kill fire blight bacteria when a copper ion that has been dissolved in water comes in contact with an active fire blight canker. A small amount of water is necessary for copper activation (air humidity can often be enough), however too much water, such as periods of heavy rainfall, will completely rinse the copper away. With fewer rainfalls expected during this year’s shortened pre-bloom period, fixed copper will need to be washed off to prevent plant damage. Even a small amount of copper residue remaining at petal fall will cause fruit russeting.

The challenge is to apply enough copper when fire blight cankers are active, meanwhile limiting the overall amount of copper that must be weathered or washed off by petal fall to prevent russeting. Although most growers planning to utilize a copper spray have already purchased a product, differences in solubility between copper formulations on the market play an important role in efficacy. Copper products that have high solubility are removed rapidly by rainfall but are prone to causing phytotoxicity, even at low application rates. Conversely, copper formulations with lower solubility are much harder to wash away, which also increases russeting risk. Solubility can be decreased with the addition of hydrated lime to soluble coppers, which reduces phytotoxicity by acting as a buffering agent. The most soluble forms of copper are bluestone copper, then copper hydroxide, copper oxychloride while the low solubility can be found in copper sulfate, pentahydrate and cuprous oxide.

With fewer rain events in the forecast, growers can choose to apply a more soluble product that will remove fixed copper from the plant surface faster. Using excessive rates of copper, especially finely ground coppers that have good residual properties, will often result in fruit russeting, so erring on the lower end of the label rate is recommended. One pound of copper per acre is recommended, however applying fewer pounds per acre may not reach the minimum requirement for activity against bacteria at bloom. Most product labels will suggest up to 2 lb. of copper per acre which should be halved. For orchards with a large mass of green tissue, 1% oil can be added to boost distribution. Warm and humid days are best for spraying to allow copper to dry onto leaves, while colder days (30-40°F) will slow progression.

Follow these links for information on Preparing Tank-mix Bordeaux Mixture and 5 Tips For Working with Copper, or check out the general guide from last week’s blog, Demystifying Copper for Disease Management.

Dormant oil concentration and timing for San Jose scale and European red mite
With a shorter pre-bloom period expected, making multiple oil applications at lower rates to target San Jose scale (SJS) and European red mites may not be possible. Instead, consider making one application of oil at a higher rate (2-3% rate dilute) on a warm day. Oil performs best when relative humidity is less than 65% and temperatures are warmer than 60°F. The most effective time to target the overwintered, immature San Jose scale is during the delayed-dormant period, from silver tip to half-inch green. Developing foliage will increase spray shadowing as the season progresses, reducing application effectiveness. Note: Do not apply oil if freezing temperatures are forecasted 24 hours before or after the target application date.  For more information on managing SJS, visit

San Jose Management: Scaling it Up as Buds Break.

Oystershell scale, on the other hand, overwinters beneath the dead-mother scale as eggs and cannot be effectively targeted pre-bloom with oil. Oystershell scale (OSS) will begin to hatch at 364-449-degree days, base 50°F. On a normal year this may occur between May 15 and June 1. We will revisit OSS management strategies in the coming weeks.