By KARI A. PETER
Green tip through first cover is a critical time to manage many apple diseases, the most important being apple scab and fire blight. Over the next month, please keep in the mind the following recommendations to successfully manage these diseases.
General tips from green tip through first cover
- From green tip through first cover, always have in your tank a broad spectrum, specifically a rainfast mancozeb (Manzate Pro-Stick, Roper Rainshield, etc.). 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 second cover; however, be mindful of the 77-day PHI for early cultivars.
- Always rotate fungicides by spraying by different FRAC groups.
- If using alternate row middle (ARM), keep spray intervals to three to four days; shorter when environmental conditions are ideal for disease development. During bloom through petal fall, use complete sprays because this is when disease pressure is the highest for both apple scab and fire blight when disease conditions are favorable. For complete sprays, do not stretch spray intervals more than seven days.
- If rain persists during the early season, fungicides must be reapplied in the rain to keep trees protected. Use broad spectrums, such as mancozeb, captan or sulfur. Avoid spraying during heavy rain; light rain and/or misting is acceptable. Expect coverage to last 2-3 days.
Green tip
Scab spores will begin to be dispersed from overwintering leaves starting at green tip; however, the spore numbers will be low, gradually increasing over time.
Management options:
- Mancozeb can be used alone at 3 lb/A.
- Tank mixing with Syllit (1.5 pt/A).
- Sulfur (8 – 10 lb/A)
- Potassium bicarbonate (3 lb/A)
Tight cluster
Tight cluster begins powdery mildew control. If conditions are dry, focus on managing powdery mildew by using products such as Rally, Topguard/Rhyme, Trionic/Procure, sulfur or potassium bicarbonate. Dry weather plus low scab spore numbers equal low disease pressure. Although some strong powdery mildew products are not as effective against scab, tank mixing with a broad-spectrum fungicide (i.e. mancozeb) will keep the disease in check. For those using low-risk programs, sulfur and potassium bicarbonate can both control powdery mildew and scab.
If disease conditions are favorable for scab (warm and wet), consider using other fungicides from FRAC Groups 3 or 9:
- 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)
Growers are highly encouraged not to use the FRAC Group 7 fungicides during this time period; these fungicides are best saved for peak apple scab pressure, which is from pink through petal fall.
Pink through petal fall
Apple scab management
Scab spores will start to peak (the maximum number of available spores dispersing from the overwintering leaves) beginning late pink and will remain high through approximately late petal fall. In our experience with monitoring scab spore dispersal from overwintering leaves, available scab spores remain high (more than 10,000 – 20,000) for approximately two weeks (from late pink through petal fall).
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)
- 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 this period of high disease pressure. A maximum of four complete applications are allowed per year for FRAC Group 7 and 11 fungicides (regardless if you a single mix or a pre-mix). Save two fungicide sprays (if possible) for the end of the season when Luna Sensation, Merivon or Pristine should be applied in order to mitigate late season and storage fruit rots.
Fire blight management
Add 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 benefit of the product. We have observed an additive effect of repeated applications of plant defense activators.
Pink
Bloom
- 10 – 20 % Bloom: Serenade ASO, Double Nickel
- 50 – 100% Bloom: Streptomycin + Actigard 1- 2 oz/A; Streptomycin + Prohexadione calcium (Apogee or Kudos; 2 - 12 oz/A depending on the tree size)
Petal fall
- Streptomycin + Prohexadione calcium (Apogee or Kudos; 2 - 12 oz/A depending on the tree size)
- Streptomycin + Regalia (2 qt/A)
- Streptomycin + Prohexadione calcium (2-4 oz/A) + Regalia (2 qt/A)Other options (still under study at Penn State): LifeGard and Vacciplant
First cover
Apple scab management
- Although the number of overwintering scab spores drastically decreases after petal fall, spores are still available and can wreak havoc, especially if conditions favorable for disease are present. During this time, use products from FRAC Group 3 and 9, tank-mixed with mancozeb or captan, depending on cultivar and PHI.
Fire blight management
- Prohexadione calcium should be applied every 10-14 days to help with shoot blight management until shoots have hardened off.
- If tree growth is desired, continue adding Regalia to your fungicide sprays or apply separate Ceuva sprays (2 qt/A). Do not add adjuvants to the tank mix when applying copper.
Source : psu.edu