Watch out for Several Fruit-Eating Pests this Fall

Jeff Rugg

Q: My apple tree has fruit that are the right size, but the few remaining apples look awful. There seems to be many problems. Some of the fruit have worms in them, some contain brown tunnels and others are odd shapes. There are bumps and bruises on the surface of some, while others are smooth. A few appear shriveled and black; leaves and fruit are falling off regularly.

What can I do besides spraying all the time?

A: Let's see if we can figure out some of these problems. Several insects affect many kinds of fruits from core types like apples to pit varieties like peaches. In other cases, the insects are more specific to one kind of fruit, but usually there is a similar insect species affecting other fruits. In most cases when trees drop fruit prematurely, they are responding to an insect or disease issue. Quite often the insect doesn't mind the drop, since it spends part of its life cycle in the soil; it falls out of the tree without being exposed to predators like birds and isn't injured.

The codling moth doesn't need to be coddled. The small, half-inch long moth lays an egg on a leaf, allowing the baby caterpillar to crawl over to the apple. It burrows into the core — you see a black center after it eats the seeds. The caterpillar also consumes some of the fruit in the apple leaving tunnels that occasionally go all the way out to the surface where large brown spots can form. If your apple has a worm in it, this is probably the culprit. After three weeks in the apple, they leave to form a cocoon on the tree branch. There can be as many as three generations a year. The caterpillar of the fall's last generation spends the winter in a cocoon.

Pick up and dispose of dropped fruit all season long; this is one of the ways apple trees try to get rid of this pest, and you can help by disposing of the fruit that still contains the caterpillars. During the fall, put traps on the tree to help eliminate the final set of caterpillars, which are the future adult moths in the spring. They are a nationwide pest on apples, peaches, plums, cherries and walnuts.

The plum curculio is a type of beetle that causes several kinds of damage. The quarter-inch long adult lays an egg by cutting a crescent-shaped slit in the skin of the tiny apple. The scar remains as the fruit matures and may become half-moon shaped. If the egg doesn't survive, the apple often develops a discolored bump at the scar site. If the egg hatches, the larva tunnels into the apple to eat the fruit. As with the codling moth, the tree will often drop the damaged fruit, which allows the larva to finish its growth in the soil. The adult stage has a snout that can also feed on the apple causing more skin harm, but no internal damage.

Picking up dropped fruit will eliminate most of the weevil's larval stage. Otherwise, a spray is probably necessary to drastically reduce a large population. Spray should be applied when the petals fall off the flowers and again two weeks later. This spray schedule will also work on the first generation of the codling moth. The plum curculio is found east of the Rockies on trees such as: apple, apricot, cherry, crabapple, hawthorn, nectarine, peach, pear, plum and quince.

The apple maggot is the larva to a fly. The adults hatch out of the soil from June until September, much later than the first two pests. The female puts eggs in the apple — each egg-laying spot could become a dimple in the surface. The larva eats its way around the fruit leaving brown tunnels.

Gather up all the fallen fruit as they drop to reduce the population. The adults can be trapped by hanging red sticky balls in the tree. Place two or three in a dwarf apple tree and at least six in a standard-sized tree. Leave them up until harvesting time. Check the traps regularly; a spray program may be created if the traps are overwhelmed. The adults feed on apples, apricots, crabapples, hawthorn, pears, plums and serviceberry. They are pests in Eastern, Midwestern and Pacific Coast states.

The last problem sounds similar to apple scab. This is a common fungus on apples and crabapples. The leaves will become discolored yellow-green spots that eventually turn brown. When there are enough spots, the leaf falls off prematurely. Susceptible trees can lose most of their leaves by August in a bad year.

The fruit go through the same routine by receiving spots first. If the spots are bad enough, a large section of the fruit will turn brown or black and appear scabby.

The fungus survives on the fallen leaves and fruit, so they need to be cleaned up in the fall. Depending on the weather, each spring is different. A fungicide spray program would start in the spring as the buds begin to open and continue weekly until the weather dries out. Spraying may need to start again in the fall if the rains return. Some newer apple varieties are less susceptible to apple scab.

When you get insect problems, it may be possible to cut out some of the fruit — save the remaining apples to make applesauce.

E-mail questions to Jeff Rugg, Kendall County unit educator, University of Illinois Extension at jrugg@uiuc.edu. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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