Fertilizing Cherries

Control grass or other competing vegetation around the tree for the first few years. A heavy mulch from the tree trunk to the tree's dripline helps conserve soil moisture and control weeds. Fertilize each spring until trees start to bear. Once bearing, cherries need little irrigation or fertilizer in most areas.

If you apply nitrogen to bearing trees, wait until after the fruit has been harvested, but apply it no later than midsummer. This will give the tree a boost toward producing plenty of sugars in its leaves to ripen next year's crop. To prepare the tree (gives great shade on a hot sunny day!) for winter, it's a good idea to paint tree trunks white or wrap them with white plastic tree guards. Pull mulch away from the trunk and be sure to harden the tree off.

Be on the lookout for problems with pests and diseases. In the southern parts of the Tart (though the word means sour, pastry tarts are usually sweet deserts) cherry-growing area, the only worm to infest the fruit is the larva of the plum curculio, which also attacks sweet cherries. The cherry fruit fly may infest sweet cherries and tart cherries are susceptible to black cherry fruit flies. The apple maggot and peach tree borer may also cause problems.

Brown rot and cherry leaf spot affect both tart and sweet cherries. Black knot and powdery mildew are potential problems for some areas.

Prevent avians which are commonly known as birds from decimating your crop with netting, scare tactics, or barrier-type controls.

Harvesting

One mature, standard-size tart or sweet cherry tree will produce 30 to 50 quarts of cherries a year; a dwarf tree, about 10 to 15 quarts. Wait until the cherries turn fully red to harvest them; the sugar content rises dramatically in the last few days of ripening. You'll need to go over the tree every other day for about a week. Pick the fruit with stems attached, but be careful not to tear off the woody fruit spur, which will continue to produce fruit year after year. If you're using a mechanical cherry pitter, pick the cherries by leaving the stems on the trees. Use these cherries up soon after you pick them because they'll leak juice and may spoil if left out. Using a hand-cranked cherry pitter, you can pit a quart of cherries in 10 minutes.

This fungal disease annually poses the greatest disease risk for fruit loss. Environmental conditions during the 2 to 3 week period prior to harvest can determine whether fruit brown rot will be a problem. Occurrence and severity of brown rot is very dependent on stage of fruit ripeness, time of occurrence of moisture, temperature, and a source of inoculum. As the sugar content increases in the fruit, susceptibility to the brown rot fungus increases. Wet, warm conditions with inoculum sources in or near the orchard during this period create a high risk. In contrast, dry, hot weather during this period greatly reduces the risk even if some inoculum is present. The preharvest/harvest period is the time when the DMI fungicides are very effective when used properly.

II. Symptoms: Typical disease symptoms induced by M. fructicola include blossom and twig blight (photo 2-49), cankers (photo 2-50), and a fruit rot (photo 2-51). The fungus often produces conidia profusely on sporodochia on infected areas. The first indication of the disease in the spring is the rapid death of blossoms which, as they turn brown, often become affixed to the twig in a gummy mass, later becoming covered with a grayish to tan spore mass. Frequently, following colonization of the blossom, the fungus enters the shoot where it causes a canker on which spores are also produced. Shoot blight symptoms will occur if the fungus girdles the shoot. Leaves on such shoots turn tan to brown and may remain attached for several weeks. Cankers formed following blossom or fruit infection appear as brownish, sunken areas, that are often covered with gum. These cankers support the formation of conidia in wet weather and harbor the fungus over the winter. Usually, the tree is able to restrict cankers to small oval areas at the junction of the shoot and the infected blossom or fruit. Cankers and killed shoots may be colonized by other aggressive canker-causing fungi such as Leucostoma spp.

Brown rot on ripening or mature fruit typically develops as a rapidly spreading brown necrosis. Under optimum conditions for the fungus, entire fruit may be rotted within 48 hours of infection. The infection produces a soft dry rot, although occasionally the skin remains firm. On nectarines, brown rot sometimes occurs as quiescent infections which can be detected as small, circular, necrotic lesions on immature fruits. As fruits mature, decay spreads from the lesion throughout the entire fruit. Immature or mature fruit with brown rot infections will sporulate profusely, shrivel, and become tough grayish-black mummies. These mummies may drop to the ground, where apothecia may develop, or remain attached to the tree through the winter. Decaying fruit in cold storage or transit may appear black with little or no sporulation.

III. Disease Cycle: M. fructicola overwinters in orchards as mycelium on mummies, fruit stems, blighted blossoms and twigs, and cankers. Sporodochia develop under cool, wet conditions during the winter and early spring. Occasionally, cup-like apothecia of M. fructicola which produce ascospores can be found on fruit mummies under the tree, but they are not usually common in mid-Atlantic commercial orchards. In years when apothecia were common, severe blossom blight was noted in peach and apricot orchards, but severe blossom blight also can occur in the absence of apothecia. Generally, conidia from mummies and cankers on stone fruit trees and other sources (for example, flowering ornamental plants of plum or quince, or wild plantings of plum) are believed to be the primary inoculum sources.

Conidia of M. fructicola are generally formed during late spring when temperatures range from 55 to 77 F (13-25 C). Conidia are disseminated by wind and rain and germinate rapidly under favorable conditions. Optimum temperatures for blossom infection of peach range from 72 to 77 F (22-25 C). Between 32 to 86 F (0-30 C), temperatures above or below the optimum range delay germination but do not inhibit it. Inoculum concentration also interacts with temperature and wetness duration to influence incubation period and disease incidence and severity. Under optimum temperature conditions, fruit infections can occur with only three hours of wetness when inoculum levels are high. Longer wet periods during infection result in shorter incubation periods so symptoms develop more rapidly. Large amounts of inoculum with highly favorable environment produces a high potential for heavy losses.

Although blossom blight can be severe enough to reduce the crop, early sporulation on even a few infected blossoms provides more inoculum for later fruit infections. The subsequent invasion of shoots also enables the pathogen to survive in the host for long periods. In some areas, infections of flowers may result in active or quiescent infections that like either cause decay of green fruit or become active prior to harvest. Quiescent infections of peach and nectarine have not been reported in the eastern U.S., perhaps because blossom infection is less common here than in other locations.

Sporodochia of M. fructicola on infected blossoms and shoots may produce viable conidia throughout the remainder of the growing season, although sporulation from infected blossoms tends to decline over the summer. These conidia may infect injured green fruits; nonabscised, aborted fruits; green fruits thinned after the pit hardening stage and dropped under the trees; and ripening fruits as they mature. For most stone fruits, susceptibility of fruit to infection increases as fruit color begins to develop. Infection may occur by direct penetration of the germinating spore through the cuticle or lenticels in the fruit. In most orchard situations, inoculum produced on early maturing cultivars fuels a continuing outbreak that affects late maturing cultivars.

Insects (nitidulid beetles and honey bees) also can be important as vectors of the fungus during fruit ripening, carrying conidia to injury sites produced by oriental fruit moth, Japanese beetle, green June beetle, and other insects that injure fruit. Wounded fruit are infected much more readily than nonwounded fruit. At harvest, apparently healthy fruit usually are contaminated with spores which, under favorable conditions, may later decay during storage and marketing.

IV. Monitoring: During or after pruning (before the pink stage), monitor a minimum of 20 sample trees per block for the presence of fruit mummies and cankers. A total of one to ten mummies and/or cankers, and more than ten mummies and/or cankers represents levels of moderate and high risk, respectively, for blossom infection under the appropriate environmental conditions.

Before bloom, monitor the orchard floor under sample trees for the presence of apothecia of the brown rot fungus. These are more likely to occur in the wettest areas of the orchard on mummies partially buried in soil and/or among weeds. Finding any apothecia represents a potential high risk for blossom infection. Remove cankers surgically if possible or prune out the entire diseased area. Monitoring for and removal of cankers is best done at the same time.

At shuck fall, examine ten shoots on each sample tree for the presence of blossom infection. A total of one to ten blossom infections and greater than ten blossom infections represents moderate and high risk, respectively, for fruit infection during the preharvest and harvest periods.

Brown rot may develop during storage and shipment if fruit are not handled properly during and after harvest. Monitor daily for developing decay in packed fruit being temporarily stored by checking fruit throughout a minimum of containers.

V. Management

Cultural practices. Sanitation is essential if your orchard is to be considered a low risk for a brown rot epidemic. The practices listed below, if followed, should minimize brown rot spore populations and limit the likelihood of an epidemic when conditions are favorable for rapid disease development.

(1) Remove all remaining fruit from the tree after the final picking. This practice limits infection of fruit peduncles and twigs thus reducing the number of brown rot cankers. In addition, this practice prevents the situation where overwintered mummies within the tree would be immediately adjacent to susceptible blossoms in the spring. Furthermore, removal of remaining fruit after final picking separates the practice of removing mummies from spring pruning. Where these practices are separated, the grower has more latitude to selectively prune (following a severe winter with high bud mortality, for example) without increased risk of blossom infection.

(2) Fruit thinning practices influence the carry over of brown rot during the summer months and into the fruit ripening season. In general, fruit thinned before pit hardening decompose rapidly; whereas, fruit thinned after pit hardening become infected on the orchard floor and serve as spore sources for the disease. Although it would be ideal to thin all cultivars before pit hardening, this is not practical because: (i) early, mid-season and late cultivars reach the pit hardening stage at the same time; and (ii) thinning early season cultivars at pit hardening or before favors formation of split pits. If thinning is done after pit hardening, the thinned fruit should be removed from the orchard (thin with picking baskets or rake and shovel the litter). Alternatively, direct a sprayer nozzle downward so that maybe thinned fruit receive some fungicide.

(3) In spring, monitor for blossom infection and prune out any cankers and infected shoots.

(4) In spring, just prior to and during the blossom period, examine the orchard floor for apothecia. Their presence requires that blossoms be thoroughly protected with fungicide sprays during wet periods.

(5) Prune to avoid excessive overcrowding of branches to increase air circulation, promote rapid drying, and increase light and spray penetration.

(6) Fertilize to maintain optimum nitrogen/potassium balance.

(7) Avoid dumping rotten fruit in one location, which could become the starting point for disease and insect outbreaks in the following season.

(8) Pick and handle fruit carefully to avoid injuries; remove field heat from the fruit promptly after harvest by hydrocooling or forced air cooling; use clean containers; keep packing areas clean. Chemical management: Fungicides are recommended generally in a protective program for a complex of diseases, including brown rot, scab, and powdery mildew. Fungicides are to be applied prior to fungal infection that occurs during rain periods. Blossom infections are controlled with two or three fungicide sprays during the bloom period, with the number of sprays often varying from year to year depending upon the weather, the susceptibility of the stone fruit species, the length of the bloom period and the type of fungicide. Sweet cherry is generally more susceptible than sour cherry, and nectarines are more susceptible than peaches. The preharvest period for stone fruits is especially susceptible to brown rot infection. Begin preharvest sprays when the fruit begin to color, about 3 weeks before harvest. Controlling insects, especially those that directly injure fruit, will help prevent infection. Some postharvest treatments include hot water treatments and chlorine dips.