Pest Alert

Sept. 21, 1999

Welcome to Pest Alert.

Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.

DISEASES

W  POWDERY MILDEW is continuing to show up on lilacs and snowberries (including coralberries). The symptoms include white to gray, dusty patches with small pinpoint-size black dots in the patches. Many of the infected leaves were infected this summer and only now as the patches have enlarged to cover the leaves are people noticing the problem. The disease is not a serious health threat to the plant but it can be unsightly. The recommended control is to remove the infected leaves in the fall. It might also be a good time to prune out the plant to allow for better air circulation next summer.

V,H SANITATION, SANITATION & SANITATION are the three keys to managing diseases for next season. Carefully clean up the leaves and other plant debris from the garden this fall, especially if the plants suffered any disease problems. Many foliar diseases overwinter on diseased plant debris from the previous season so removing this material reduces future problems. If you don’t physically remove the material, plowing it under will work well too. However, rototilling the garden will only bury some of the debris and leave much of it at or near the soil surface where it can start disease problems for next season. Organic waste from the garden makes excellent material to add to the compost pile. And, as long as the pile is active, the material will be safe to incorporate back into the garden next season as compost. For additional information on composting see ExEx 6004 - Composting Yard Waste and ExEx 6005 - Recycling Lawn and Yard Waste.

W  SEPTORIA LEAF SPOT is showing up on cottonwood trees across the state. Infected trees are easily identified at this time by cottonwood shelterbelts with only foliage near the very top of the trees. The disease overwinters in dead leaves and twigs. In the spring, during wet weather, the leaves on the lower branches become infected. Later, secondary infections continue to infect higher foliage. Usually by late summer, most of the leaves, except for those at the very top, have turned yellow and fallen. As with most fungus disease now is not the time for control. The only recommended control at this time is to remove and destroy infected leaves.

 INSECTS

F RASPBERRY CANE MAGGOTS have been a problem in several gardens in the Rapid City area. The typical symptoms include canes that wilt down and break off, usually at the base or near a swollen area on the stem. Typically, the upper part of the shoot will have exhibited some purple and brown discoloration of the stem as well. Careful, close examination of the swollen areas will reveal very tiny feeding galleries, just beneath the bark. These tunnels are filled with frass, a sawdust like material. The maggots are actually very small and may be difficult to find. The adult, which is about 1/2 the size of a housefly, emerges from infested canes in the srping and lays the eggs in the leaf axils. The larvae hatch and tunnel into the stem and begin feeding and tunneling toward the base of the plant. At the end of the summer, the larvae pupate before emerging again the next spring. (close-up view of very small feeding galeries in lower stem). The main treatment involves removal of infested canes, cutting close to the soil line. Destroy or at least remove the canes from the garden area. Protective insecticidal sprays, applied to the young canes in the spring may be helpful.

OTHER NOTES

V ASPARAGUS FERN GROWTH AND RHUBARB should be allowed to remain on the plant until it freezes this fall. It can be removed this fall or it may be beneficial to let it remain until spring. The fern growth will act to catch snow during the winter which will provide extra winter protection and moisture for next year’s crop.

L BROWN BUFFALO GRASS LAWNS will soon be a common sight when the cool and frosty weather arrives. Also, people that have other warm season grasses like zoysia or blue gramma will see their lawns browning up too. Some lawns have already turned brown. If someone knows they have a buffalo grass lawn, they are probably expecting their grass to go dormant as temperatures get below 50°. However, for some homeowners, that may only have a patch of this warm season grass in their lawn, it may be quite disturbing. Buffalo grass typically grows in patches, is a lighter green than bluegrass, has small flattened seed heads and spreads over the ground by stolons. It can make a fairly nice, low maintenance lawn in some areas. But, it does brown-up early in the fall and is slow to green-up in the spring.

One significant benefit to this early dormancy is that it provides a very safe treatment window to control unwanted vegetation including broadleaf weeds and even cool season grasses. Roundup can be applied after the buffalo grass is completely brown to selectively control these unwanted plants.

W  FALL NEEDLE DROP IS OCCURRING NOW. The fall coloring and loss of inner foliage is a natural occurrence of evergreen trees, including juniper (cedar) and arborvitae. The normal shredding of needles is most apparent on pines and spruce and results in numerous calls from alarmed tree owners. The critical factor is the age of the affected needle. Healthy pines retain their one- and two-year old needle while shredding their third. Healthy spruces retain their one- to six-year old needles while shredding their older ones. However, we have been receiving calls from people concerned about excessive needle loss on spruce. Generally this is due to a combination of normal interior needle drop and the loss of current and one-year old needles from rhizosphaera needlecast disease. Usually the interior needles merely turn yellow before falling, the needles infected with needlecast turn a purplish-red before falling. There is no recommended control of needlecast at this time of year. Control is initiated in the spring just as the new growth begins.

F,V,H FROST. Freezing temperatures have arrived in most of the state and caused a flurry of calls in Extension offices around the state. Here are few answers to some of the more common questions. HOW COLD CAN IT GET BEFORE I HAVE TO BE CONCERNED? The usual killing frost is thought to be 28° but this will vary depending on the kind of plant we are talking about. Many of our tender bulbs, like cannas, will have their foliage killed at 32° while many varieties of apples can tolerate 25°. WHAT SHOULD I DO WITH MY APPLES, PEARS AND PEACHES? If you still have fruit on your trees and temperatures are predicted to get near or below 28°, the safest bet is to harvest all the fruit, especially peaches. While fruit can be even frozen solid and still be OK if it thaws out slowly, storage life will be shortened dramatically. Pears should be harvested before they are fully ripe to avoid the development of stone cells that make the fruit taste gritty when ripe. HOW DO I STORE MY HARVESTED APPLES AND PEARS? Both of these fruit are best stored at about 35° in plastic bags with a few air holes. Usually an old refrigerator works best but they can be stored in a garage as long as they don’t get too cold and the garage doesn’t get too warm later this fall during warm spells. SHOULD I PICK MY PUMPKINS AND SQUASH? If temperatures are predicted to get near of below 28°, harvesting is probably the best answer. Mature pumpkins and squash can take a pretty good frost , especially if they are covered with a blanket early in the evening before temperatures drop. However, if the skin is damaged by frost, storage life will be greatly reduced and they will soon probably begin to rot. HOW SHOULD I STORE MY PUMPKINS AND WINTER SQUASH? These vegetables are best stored in a cool (50 to 55° ) and dry location. Normally, mature, hard-skinned pumpkins and squash can be stored for two months or longer under good conditions. SHOULD I HARVEST MY CARROTS AND POTATOES? You certainly can harvest these vegetables now if you want but they will probably be OK out in the garden yet for a few weeks. Carrots can even remain in the garden all winter long if they are heavily mulched to prevent the ground from freezing. Carrots should be topped and stored in barely moist sand or peat moss (95% humidity) at about 32 to 35° for best results. Potatoes should be stored in an absolutely dark location at 40° and 80 to 95% humidity for best results. WHAT DO I DO WITH ALL OF MY GREEN TOMATOES? This is probably one of the more commonly asked questions. Mature green fruit, that is just starting to change color from green to white, can be ripened indoors. Lay the fruit out in a single layer on a flat surface. Cover the fruit with a couple sheets of newspaper. Check the fruit from time to time and remove them as they ripen. This method will work better than ripening them on a window sill because it helps to concentrate the ethylene gas that aids ripening. Plants may also be pulled from the garden and hung in the garage. Many of the fruit may still ripen. CAN I JUST COVER MY FLOWERS OR DO I HAVE TO DIG THEM UP? Covering flowers like geraniums and impatiens will help for a light frost but not a hard frost. So, I you have plants you want to save, I would suggest either digging them up now or take cuttings to keep over winter. DO I HAVE TO DIG MY GLADIOLUS AND CANNAS? You can still wait to dig these tender bulbs. It is usually best to wait a week after the tops are killed by frost before digging.

L  LAWN FERTILIZATION is best done in the fall, especially for those lawns that are not highly maintained, i.e. watered all summer, clippings are removed and the grass is mowed fairly short. One or two applications should provide most of the low maintenance lawn’s nutrient needs for the next year. Apply 1 lb. of actual nitrogen per 1000 sq. ft. now and again, if desired in 4 to 6 weeks. An ordinary, quick-release lawn fertilizer is all that is really needed but a fertilizer that has about 25% slow release nitrogen can be beneficial. "Winterizer" fertilizers, which are lower in nitrogen and higher phosphorous and potassium are not really necessary unless your lawn is deficient in these nutrients. However, a complete fertilizer should be used, one that has a ratio of 4:1:2 will work well. Applications of nitrogen are rapidly taken up by the plant, stored for winter and Fall utilized next spring for new growth. Fall nitrogen applications generally will NOT cause a huge flush of top growth because the plant is naturally slowing down top growth at this time of year.

H PERENNIAL FLOWER FOLIAGE should be allowed to remain on the plant until the foliage has died down naturally. This will provide for the maximum amount of food to be stored in the plant’s crown to better enable it to get through the winter and produce a good crop of flowers next year. It is true that the foliage can be removed earlier in the season with good results but a good general guideline is to wait until the end of the season.

Foliage removal is a major part of general garden sanitation which is especially important if the plants suffered from any foliage diseases this season. Iris and hollyhocks can benefit especially from this fall sanitation since they are prone to diseases that overwinter on the old foliage. Hollyhock rust has been very common this year with the wetter weather as has iris leaf spot. Thorough cleanup this fall may delay the onset of the disease next year.

W WATERING IS STILL A GOOD IDEA FOR TREES AND SHRUBS. In many parts of the state we have had limited precipitation during August. Some people are concerned that watering during late summer will delay hardiness and increase winter injury. While this can occur if marginally hardy trees are provided with luxurious amounts of water during late summer this is the exception rather than the rule. Instead, providing trees and shrubs with water will usually not delay dormancy and can increase winter hardiness. How much water is enough? Here is the typical weekly water use for various diameter trees; a 1-inch diameter (diameter measured 4.5 feet above the ground) requires 20 gallons, a 2- inch diameter tree requires 35 gallons and a 5-inch diameter needs 125 gallons of water every week.  

W  WE ARE GETTING CLOSE TO THE BEST TIME TO FERTILIZE TREES AND SHRUBS. Fertilizing after the first hard frost will allow time for the tree to absorb and utilize the nutrients this fall. Fall fertilizing will not result in an expansion of shoot growth, or a reduction in winter hardiness. Fall fertilizing will improve spring growth, however, as 70 percent of the nutrients used in the construction of spring growth are absorbed during the previous fall.

W  WHY ARE MY TREES DROPPING THEIR LEAVES NOW? We sometimes get this question from tree owners concerned that their tree is dropping leaves before the others in the neighborhood. There are several reasons to explain this and not all of them indicate a problem.  It might be a tree species that drops leaves earlier than the others.  Black ash, Kentucky coffeetree, and black walnut are all examples of trees that drop their leaves earlier than most trees.   It might be due to drought.  Trees in most of New England were dropping their leaves in late August due to the extended drought occurring in the region. If the tree is not able to provide water to the foliage it will begin to shed the leaves prematurely. While most of the state has been receiving adequate moisture, there are a few areas that still have not received much precipitation since July and in some of these areas (such as parts of southcentral South Dakota) many trees have having the leaves turn yellow and drop.

It may be due to a fungus. A number of trees, most notably ash, walnut and oak, have anthracnose. This is a fungus disease that results in botches forming on the leaves and often the leaves dropping prematurely. There is no recommended control at this time other than removal of the infected, fallen leaves. While it may not be a great help in controlling the disease and can provide some reduction of spores the following spring.

V WINTER SQUASH AND PUMPKINS should be harvested before frost for best storage. Cool temperatures, below 40F can cause cold temperature injury to the fruit which can shorten storage life. Frost can cause more severe injury, especially if the fruit are not fully mature.  Frost damage can result in the invasion of decay organisms resulting in rapid softening and spoiling of the fruit. For maximal storage life, allow the fruit to fully ripen which is evidenced by good skin color a hard shell and often the development of a yellow or orange ground spot on the bottom of the fruit (generally seen on squash). Cut the fruit from the vine with a pruning sheers to maintain the stem and carry fruit by the bottom and not the stem. If the stem breaks off, this creates a wound that allows decay pathogens to enter the fruit. Cure the fruit in a warm and dry location for a couple weeks before putting into storage at about 40F and 50% RH. Properly harvested, cured and stored fruit should store for 2 to 4 months.