Pest Alert

Sept. 15, 2000

Welcome to another issue of 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  Black spot on elms and oak anthracnose is showing up on trees throughout the eastern part of the state.  While the weather is now dry – too dry – in this region, there was also a very cool and moist spring, particularly May.  This provided ideal conditions for many leaf diseases that are only now showing symptoms.  The symptoms on the elms include small black dots surrounded by larger brownish blotches.  The infected leaves are now falling and the symptoms are sometimes confused with Dutch elm disease.  Typically leaves falling from trees infested with Dutch elm disease are wilted, dry and browning throughout rather than covered with blotches.  However, it is possible for a tree to be infected with both diseases.  Oak anthracnose, mostly found on bur oak rather than northern red or pin oak, generally results in blotches occurring along the margin of the leaves.  We have had several calls from concerned homeowners believing their oaks were infected with oak wilt.  Fortunately this disease is extremely rare in South Dakota, there have only been a few reports from the eastern fringe of our state.  Generally trees infected with oak wilt have the wilted, brown leaves that fall earlier in the summer.

W  Sulfur fungi are beginning to form fruiting bodies on the sides of decayed trees or rotted logs.   The fruiting bodies form bright sulfur-yellow shelves that may be 10 or more inches wide and extend 4 inches out from the trunk.  Sulfur fungus is one of the “foolproof four”, an edible fungus that is difficult to confuse with poisonous ones (and is delicious!).  HOWEVER DO NOT USE THIS DESCRIPTION AS YOUR GUIDE FOR MUSHROOM HUNITING, ALWAYS HAVE THE MUSHROOM IDENTIFIED BEFORE EATING IT!

INSECT CONTROL

W  Asian  longhorned beetle sightings in South Dakota picked up quite a bit during August, due in large part to the Sturgis motorcycle rally.  A number of bikers from the Chicago area – an area that has an infestation, hence tremendous press coverage – thought they found the beetles in the Hills.  In each instance that we are aware of, the suspected Asian longhorned beetle turned out to be a pine sawyer.  While these were “false alarms” it was appreciated that some people were concerned enough about the possible threat of the beetle to take the time to report a finding.  On a related note, the quarantine boundaries in the Chicago area may be extended due to the capture of adult longhorned beetles outside the quarantined zone.  The Asian longhorned beetle is a recent introduction from China.  It is a serious pest of hardwoods, particularly poplars and soft maples.  There is no control except removal and burning of infested trees.

 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 tree care.  We are coming up to the best time for fertilizing trees – beginning with the first hard frost – and this subject will be discussed more in the next Pest Alert.  While it is a little early to fertilize, it is an excellent time to irrigate.  Trees that enter winter too dry are more susceptible to winter injury, not less.

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 windowsill 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 that 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.

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 that can shorten storage life.  Frost can cause more severe injury that 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 that 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.