2022 Disease Update: Bloom Recommendations

Mother nature has had trouble making up her mind if she wants to channel winter or spring these days. She appears to be channeling summer-like conditions this coming weekend based on the upcoming forecast. Since the number of available overwintering apple scab spores are close to peaking, disease pressure could be high if optimal conditions occur—wetting conditions with at least 6 hours of wetness.

The warm weather during bloom may also favor fire blight conditions. The current forecast is still not certain about a wetting event. However, the temperatures will favor bacterial growth in the flowers. Apple bloom is a tough time for many diseases, so stay on your toes.

Apple Disease Management: Pink Through Bloom

As I have been advocating for a few years, green tip through first cover should include a rainfast mancozeb (Manzate Pro-Stick, Roper Rainshield, etc.). The rainfast quality of the mancozeb gives better disease control since it can persist longer during rainy, wet periods. Any non-rainfast mancozeb can be made rainfast by adding a spreader sticker (4 fl oz/100 gal). In some cases, mancozeb could be extended to the second cover; however, be mindful of the 77-day PHI for early cultivars.

For growers using captan during the early season, a spreader sticker is not recommended since captan is already has a "rainfast" quality. No additional spreader sticker is necessary if you are using a "captozeb" mix of captan plus mancozeb. However, considering supply issues with captan this season, growers may want to conserve their captan supply during the early season and save it for summer cover sprays. If you choose to use ziram, instead of mancozeb or captan, adding a spreader sticker will make it rainfast.

Apple Scab Management

Growers are highly encouraged to use complete sprays instead of ARM from bloom through petal fall, especially if frequent rain events favor extended wetness periods. During this time, it is best to use FRAC Group 7, 7 + 9, 7 + 11 fungicides:

• Aprovia (FRAC Group 7; 5.5 fl oz/A)
• Excalia (FRAC Group 7; 3 – 4 fl oz/A)
• Fontelis (FRAC Group 7; 16 fl oz/A)
• Miravis (FRAC Group 7; 3.4 fl oz/A)
• Sercadis (FRAC Group 7; 4.5 fl oz/A)
• Luna Tranquility (FRAC Groups 7 + 9; 11.2 fl oz/A)
• Luna Sensation (FRAC Groups 7 + 11; 5 fl oz/A)
• Merivon (FRAC Groups 7 + 11; 5 fl oz/A)
• Pristine (FRAC Groups 7 + 11; 14.5 – 18.5 oz/A)

When necessary, rotate FRAC Group 7 fungicides with the following:

• Cevya (FRAC Group 3; 5 fl oz/A)
• Indar (FRAC Group 3; 8 fl oz/A)
• Inspire Super (FRAC Groups 3 + 9; 12 fl oz/A)
• Scala (FRAC Group 9; 5 – 10 fl oz/A)
• Vangard (FRAC Group 9; 5 oz/A)

Limit FRAC Group 7 and 11 fungicides to two complete applications during high disease pressure. A maximum of four complete applications are allowed per year for FRAC Groups 7 and 11 fungicides for fungicide resistance management (regardless if you use a single mix or a pre-mix). Save two FRAC Group 7 and 11 fungicide sprays for the summer and late-season to manage rots.

Note for bitter rot management: Bitter rot is not critical during this period since the disease pressure is considered low. A strong apple scab protection program will suppress any bitter rot spores in the orchard. The time for bitter rot control will need to be from June through late harvest, and control needs to be applied prior to any wetting event.

Fire Blight Management

As a reminder, the minimum requirements for blossom infection and the order in which they must occur are:

1. Flowers must be open with petals intact (flowers in petal fall are resistant)
2. An accumulation of at least 198 degree hours above 65ºF
3. A wetting even as dew or rain
4. An average daily temperature of 60ºF

There are many NEWA stations in Pennsylvania, and growers can refer to the nearest one to their location to double check the risk for fire blight.

The following strategies will also help control fire blight in pears.

When conditions are forecasted to be favorable for fire blight, consider applying products that activate plant defenses to your fungicide sprays to help get a jump start on management, especially since it takes approximately 48 hours to observe the product's benefit. We have observed an additive effect of repeated applications of plant defense activators (applying every 3-5 days).

Tight cluster

Especially if warm weather is moving trees along quickly.

• LifeGard 4.5 oz/100 gal
• Vacciplant 16 fl oz/A
• Apogee/Kudos 6 oz/A (only apply to high vigor apple trees; not labeled for pears)

Pink

• Actigard 1 – 2 oz/A
• LifeGard 4.5 oz/100 gal
• Vacciplant 16 fl oz/A

• Reminder: Actigard, LifeGard,and Vacciplant need to be applied within 48 hrs. of an infection event for the defenses to be activated.
• Apogee/Kudos 2 oz/A (only apply to high vigor apple trees)

Bloom

• Streptomycin remains the best option for management.
• For added protection – combine strep with Actigard, LifeGard, or Vacciplant
• A typical streptomycin application gives you 48 hours of protection.
• When applying streptomycin, you are killing the bacteria within the flower at that moment and resetting the clock. It is important to apply treatments before any wetting event to eliminate the potential for bacteria to enter the flower nectaries.
• Include a plant defense elicitor or Apogee/Kudos in your streptomycin application for added protection.
• Organic management options include Blossom Protect or Regalia 1 qt/A plus Magna-Bon CS 2005 1 pt/A. Blossoms must be open, and these products must have been applied before the anticipated infection event to be effective.
• Using copper products with copper sulfate pentahydrate is probably the best copper option for fire blight management because this is a soluble copper. All the copper ions are present to kill the bacteria when applied. In contrast to fixed coppers, where the copper ions are released gradually. Please note that all copper products have the potential to cause fruit finish issues.

Commercial fruit growers, please note

When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one's own orchard. To assist with management decisions (especially infection events), growers can use the NEWA website, which has weather stations all over Pennsylvania. Before chemical products are applied, be sure to comply by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from CDMS.