Each season, apple diseases are a threat to home orchard productivity and fruit quality. Now is an important time to manage some of these destructive diseases. There are many cultural practices that can be implemented now and in the coming weeks to reduce the threat of diseases such as apple scab, fruit rots, powdery mildew, collar rot, fire blight and cedar-apple rust.
The following are cultural practices beneficial for reducing apple diseases:
Prune out last year's infections, cankers and any dead wood while the trees are dormant. Dead and diseased wood provide a reservoir for spread of fungi and bacteria to nearby healthy trees or parts of trees.
Remove nearby landscape or forest trees or overhanging tree branches that might shade the fruit trees. Shade on apple trees means that susceptible leaves will remain wet longer following rain or dew, thus increasing the chances of infection by disease-causing fungi.
For apple and pear disease management, especially fire blight, remove and destroy any abandoned and unsprayed apple or pear trees. Fire blight, a bacterial disease, was severe locally last year in many Kentucky orchards and backyard apple and pear trees. If the disease was serious last year, extra measures may be needed. Very early season (dormant to silver tip) applications of fixed copper sprays are helpful in fire blight management. These sprays serve to reduce epiphytic (tree surface) populations of pathogenic bacteria in the orchard. Apply copper sprays to the entire orchard, including cultivars not considered susceptible to the disease. The reason for treating non-susceptible cultivars is that even cultivars that normally are not very susceptible to fire blight, such as Red Delicious, can be colonized by fire blight bacteria and serve as a source of infection to other, more susceptible trees during bloom.
Remove and destroy nearby susceptible cedars and junipers if possible, or at least remove and destroy galls on cedars and junipers too valuable to cut down. Cedar-apple rust galls are visible on cedar twigs and branches now, appearing as brown, somewhat-spherical galls an inch or two in diameter. They will be even more visible during moist periods next month when the orange, gelatinous telial "horns" appear. If cedars or junipers are not present within 200 yards of the orchard, cedar rust diseases are not likely to be a serious problem for the orchard.
Thin apple tree branches during dormant pruning to open up the trees for better sunlight penetration. Again, speeding up leaf surface drying reduces chances for foliar diseases. Remove prunings from the orchard and destroy them. The pathogens in those dead and dying branches can be moved by insects, wind, and rain back into the orchard if left nearby.
Mummies (dried, shriveled fruits from last year) should be removed from the tree, picked up from the ground and destroyed. Many of these mummies contain disease-causing fungi which could start a new epidemic.
Rake up and destroy all fallen leaves from the previous season or chop fallen leaves into tiny pieces with a power mower before spring. The fungus that causes apple scab overwinters on fallen leaves and develops spore-producing capability in the spring. Removing the previous season's diseased leaves or chopping them up finely is an important step in apple scab management. A mulch mower, used in the orchard before April, can reduce the risk of scab considerably (perhaps 80 to 90 percent) if all of the leaf litter is shredded.
Incorporate apple disease resistance into the orchard disease management program by selecting scab-resistant apple trees, fire blight-tolerant apple varieties and rootstocks and collar rot-tolerant rootstocks.
Use only disease-free nursery stock when planting new trees.
Provide good soil drainage.
Remove and destroy weeds, undergrowth and brush from near the orchard; these plants may harbor pathogenic microbes.
Springtime is the most important time to prevent diseases. By preventing early-season primary infections, secondary infections are also avoided. Purchase necessary fungicides so that they are available when they are needed during the growing season. For more information contact the Extension office at 270-886-6328 for a copy of the publication Disease and Insect Control Programs for Home Grown Fruit in Kentucky Including Organic Alternatives (ID-21).
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.