AppleTalk Conference Call Summary
Tuesday, July 14, 2015, 8:00 – 9:00 AM
Guest speaker: Patty McManus, Department of Plant Pathology, University of Wisconsin
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,
July 14th Call download: Click Here
Can you review management options for fire blight after hail storms and how to manage existing cankers? We have orchards in the region which received 100% hail damage, how could we use copper in these orchards to suppress fire blight bacteria from cankers, where we are not concerned about crop quality, e.g., russeting?
• It is important to apply streptomycin within 24 hours of a hail event to prevent infection of Erwinia bacteria. The 24 hour application window is not substantiated by research, rather is a best guess on the infection timing. If there are active fire blight strikes or cankers within the orchard it is critical to make the application within a day. If fire blight is not active in the orchard or if weather conditions do not allow for an application within a day streptomycin applied after this time is not likely to help.
• As apical buds begin to set, the concern for shoot blight decreases.
• Copper primarily functions by contact and will have surface activity on actively oozing cankers, fruit or shoots. It has less systemic activity than streptomycin and is not recommended to apply immediately following infection.
• Dr. McManus is uncertain if foliar fertilizers will promote the healing of vegetative tissue. Growers who received serve hail or have active fire blight strikes should stop their nitrogen fertility program and should not apply anything that will promote additional growth, especially on vigorous trees.
Life cycle and management of summer fruit rots, e.g., bitter rot. Where does this pathogen over winter? Are orchard that received hail more susceptible? Will high amounts of fruit rot this year, overwinter in the orchard and increase inoculum for next year?
• Dr. McManus is unsure of any research done to determine the susceptibility of apples to fruit rots following hail damage. She completed research on cranberries and simulated hail injury by shooting pea gravel at the cranberry planting. Only very shortly after bloom, when fruit was very young, was an application of a strobilurin (QoI) found to prevent fruit rot on cranberry. The fruit rot found in cranberry is very similar to pathogen that causes bitter rot on apples. Copper and Bravo (chlorothalonil) were found to prevent further infections caused by this pathogen.
• Fruit with cracked or broken skin may not be marketable at harvest due to food safety requirements.
• Fruit left on trees will be a source of fungal inoculum for next year. If bitter rot is present in the orchard, it can overwinter on the orchard floor, or in trees on mummies.
• If rotten fruit is found inspect the lesion and fruiting bodies. If it is not sporulating place in sealed Tupperware with wet paper towels to induce sporulation. Note: fungi do not typically produce spores if weather is hot and dry.
• Characteristics of bitter rot, fruit:
o Generally takes several weeks following infection before symptoms develop, may become visible before other rots.
o Symptoms first appear as small, light-brown, circular spots. Many spots per fruit may be found.
o Under high temperatures initial lesions may rapidly enlarge and change to dark brown in color.
o 1/8 to 1/4 inch in diameter lesions are distinctly sunken or saucer shaped.
o When lesions reach 1/2 inch in diameter, small, black fruiting bodies appear in the sunken lesion. Fruit bodies may be arranged in concentric rings.
o Fruiting bodies will begin to ooze a gelatinous, salmon-pink mass of spores, which is washed by rains onto other fruit.
o Beneath the surface of the spot, the flesh is light brown and watery in a cone or V-shaped area, with the small end of the cone toward the fruit center.
o Cankers can form on vegetative tissue, but are rare.
• Characteristics of black rot, fruit:
o Black rot infections on fruit usually appears at the calyx end and can originate at any wound that penetrates the epidermis, e.g., insect or hail injury.
o Usually only one spot occurs per fruit, a characteristic that distinguishes black rot from bitter rot.
o Initial infection becomes brown and stays brown or turns black as it increases in size.
o A series of concentric rings often forms as the rotten area increases in size. Lesions are usually amorphous. The flesh of the decayed area remains firm and leathery. Fruiting bodies will appear on the surface of the rotted tissue.
• Fungicides that will offer protection against fruit rots include captan, strobilurins, e.g., Pristine (boscalid, pyraclostrobin) and Flint (trifloxystrobin), and Topsin. Do not apply strobilurins if scab lesions are present. A high rate of captan may provide adequate protection. Note: to reduce resistance concerns always tank-mix single-site fungicides with a protectant.
Sooty Blotch and Flyspeck. Growers should have made their first application for SBFS, can you review the reapplication interval? How much reach back do different fungicides offer? If protecting for SBFS with captan, how long will this residue provide control for?
• Beginning around fall, the first influx of spores are released from wood lots, e.g., raspberries. This typically occurs during first cover when scab fungicides are still be applied. After about 175 hours of leaf wetness, sporulation will occur and result in the second spore release. This can happen between three and 11 weeks post-bloom, with an average of seven weeks post-bloom. It is important to apply a fungicide for summer disease at this time. Follow the first application with a protectant program. The reapplication interval following the first application is dependent on rainfall and weathering of the material. A 2-3 lb. rate of captan is greatly reduced after two inches of rain or 14 days, higher rates may offer added protection.
• Dr. McManus’ research on summer disease focused on the development of a summer disease model for the upper Midwest. Relative humidity (RH) was used rather than leaf wetness hours (LWH) to predict infection periods. It was found that 192 hours of RH above 97% was a better predictor than 175 hours of leaf wetness for our region. During the summer, dew usually contributes to more wetting hours than rainfall. Within the tree canopy, RH is more stable. Regardless of research Dr. McManus recommends using LWH because the instruments are more precise. It is important to place the leaf wetness plates within the canopy to accurately record LWH.
• Fungicide performance was greatly improved when appropriate coverage was achieved. Increasing the amount of water applied per acre can greatly improve coverage. Large semi-dwarfs or standard trees may require up to 100 gallons water per acre if canopies are dense and air circulation is poor. Using a higher rate of fungicide will also improve protection.
• Do not apply strobilurin or DMI if scab is present. It is recommended to apply high rate of captan or captan and Topsin.
Insect
Japanese beetle
A new strain of Bt (Bacillus thuringiensis) that can be used in organic and conventional orchards for control of Japanese beetle has been registered in Wisconsin. For more information: Phyllom BioProducts, beetleGONE! Historically when making applications for Japanese beetle nerve toxin
Codling moth
Continue to monitor codling moth (CM) traps as first generation flights are ending. Spot sprays or partial block sprays can be used to target locations where moths are continuing to be caught over threshold. First instar CM larvae are beginning to be found in fruit.
Apple maggot
Apple maggot emergence has begun across the region. Monitor traps, increase trap density if no AM are captured.
Obliquebanded leafroller
Insecticide applications targeting obliquebanded leafroller (OBLR) will help prevent large populations in August. Scout for leafrollers in cultivars with water sprouts, e.g., Cortland, or young trees that are still growing. If a lot of large OBLR are present note that resistance to CM materials, e.g., diamides (chlorantraniliprole) or spinosyns (spinetoram), is beginning to be observed.
