Home Garden Disease Control Begins This Fall
PP-737 (Revised), Reviewed July 1996
H. Arthur Lamey, Extension Plant Pathologist
Cynthia Ash, Diagnostician
- Vegetables
- Apples
- Other Fruits
- Ornamentals
- Lawns
- Trees and Shrubs
- Disposal of Plant Refuse
- Fall Application of Lime Sulfur
- Checklist of Fall Activities
When the autumn leaves have fallen from the trees and frost has killed the tomato vines, most homeowners are ready to forget about plant diseases until next summer. Actually this is the perfect time to start controlling next year's diseases. A little work in autumn can prevent a lot of trouble next summer! Why is this so? A fall cleanup of the yard and garden removes plant refuse on which many plant disease organisms (called pathogens) survive the winter. This cleanup, called fall sanitation, reduces the number of pathogens next spring, so it will take longer for pathogen populations to build up to damaging levels. A general cleanup of dead leaves and annual plants is needed. Here are some specific suggestions that are especially important.
Vegetables
Remove unproductive plants and continue weed control in late summer, since these old plants and weeds harbor diseases and insects. After a killing frost, make a total cleanup of all plants still in the garden. Take special care to remove all tomato and potato vines as well as fruits and tubers; all parts harbor blights that may cause severe losses. Be sure to remove all vines and fruits of cucumber, melon, and squash. Continue control of the cucumber beetle (Figure 1) into fall, as the bacterial wilt pathogen overwinters only in the cucumber beetle. If corn smut was a problem, destroy (by burning, burying or depositing in a sanitary landfill) all smut galls to reduce the amount of overwintering smut. After cleaning up all the crop refuse, spade or rototill the soil to bury any remaining bits of crop refuse.
Figure 1. Striped
cucumber beetle.Apples
Check for fireblight that has moved from fruit spurs or suckers into main branches one or more inches in diameter - this is done most easily after the leaves have fallen from the trees. The diseased suckers can be identified by the curled ends of the suckers and the dark brown to blackened leaves that hang on the suckers after the tree has lost the rest of its leaves (Figure 2). Diseased fruiting spurs will have shriveled fruits on them. Check at the base of the diseased sucker or spur. If the bark on the main branch is sunken and slightly discolored around the base of the sucker or spur, the disease has penetrated into the branch. Mark the edge of the discolored bark, as this branch must be removed or the diseased portion cut out, as described in Circular PP-454, "Diseases of Apples and Other Pome Fruits." This should be done in the dormant season, preferably in March or early April before the sap starts to run. Be sure to disinfect pruning tools as described in Circular PP-454. Be especially careful to prune or cut disease out of main branches -- failure to do so will result in these branches being girdled and dying.
Figure 2. How to
identify a fireblight canker. Note the shriveled spur and the dark sunken bark on the main
branch at the base of the spur. The edge of the canker is indistinct and hard to
recognize.
Prevent sunscald by applying white interior latex paint to the southwest side of the trunk and main branches, or by using other effective shading materials described in Circular PP-454.
Rake up and destroy all apple leaves in the fall, since the apple scab fungus
overwinters on these dead leaves.
Other Fruits
Rake up and destroy leaves of all fruit trees and small fruits, taking care to also destroy any rotten or dried up fruits still hanging on the tree or bush. If not done earlier, all black knot (Figure 3) cankers should be removed from chokecherries and plums, pruning several inches below the knot as described in Circular PP689
Disease Control in Cherries, Plums and Other Stone Fruits (1991) Cut out all diseased raspberry canes as well as all two-year-old canes that bore fruit this summer. Protect cherries and plums from sunscald, as described for apples.
Figure 3. Black knot of
chokecherry.
Ornamentals
Remove and destroy all annuals. Cut out and destroy all diseased rose canes and destroy all rose leaves. Spray with lime sulfur before mulching or burying non-hardy roses for the winter. If you had peony blight, cut off all peony plants level with the ground and destroy the tops after a killing frost - this will reduce the danger of peony blight next year. If your peonies did not have blight, you could leave the tops to catch snow, then cut them off level with the ground in early spring before the new shoots appear. Similar treatment of other herbaceous (non-woody) ornamentals will help prevent disease carryover.
If white mold killed some of the flowers, special care is required during their removal. Details on white mold and its control are contained in Circular PP-899, "White Mold of Vegetables and Ornamentals." Plants that are killed by white mold are best removed and destroyed as soon as possible. If you delay removal, the soil may be contaminated with the hard black bodies of the white mold fungus. These bodies survive long periods in the soil. When removing white mold diseased plants, watch for these hard black bodies and remove as many as possible.
Lawns
Don't fertilize your lawn between mid-July and mid-September. Fertilization done in late September promotes turf root development, but does not stimulate lush growth of the blades and does not promote snow mold. This procedure gets the lawn ready for next spring but reduces the number of late summer mowings and waterings needed.
Fertilizer applications during the hot season can stress lawns and result in serious lawn disease. Late July or August applications may promote snow mold in years with heavy November snows. Keep the lawn mowed and raked in the fall, since snow molds develop more readily when thick mats of grass are buried under the snow. However, mowing should not be shorter than normal; close mowing or "scalping" will not permit good root development in the fall.
Trees and Shrubs
If ash or oak anthracnose (Figure 4) was serious, rake up and destroy all leaves from these trees. Remove and destroy small branches with severe anthracnose cankers. Similarly, if any other tree species has a serious leafspot problem, rake up and destroy the leaves. Thin barked trees such as mountain ash and silver maple need to be protected against sunscald, as described above under "apples."
Figure 4. Ash
anthracnose.
Unless there was good rainfall in early autumn, be sure to water all evergreen trees
and shrubs heavily just before freeze-up. This is very important because evergreen needles
continue to lose water through the winter, but the rate increases rapidly on warm sunny
days in late winter when the roots are frozen and unable to take up water. If the plants
are low in water, the needles can dehydrate and be killed rapidly. When watering trees and
shrubs be sure to apply at least 3 inches of water. An inch of water soaks down 5-6 inches
in dry soil, so 3 inches will soak down 15-18 inches; this is the minimum needed to reach
the roots. When larger trees or shrubs are watered with a sprinkler, an old coffee can may
be placed under the sprinkler to measure the amount of water delivered. Trees and shrubs
can be effectively watered using a root feeder that injects water into the root zone. A
soaker hose can also be used. On small evergreens, the hose can be allowed to trickle at
the base of the tree for half a day or longer. An application of an antidesiccant may
reduce dehydration of evergreen needles. It should be applied just before freeze-up.
Disposal of Plant Refuse
Home gardeners frequently ask if they can compost plant refuse. Most foliar (leaf) pathogens are destroyed rather quickly once crop refuse is in contact with soil and the refuse rots. However, some soil borne pathogens, such as the wilt diseases of tomato, are soil inhabitants and are not destroyed by contact with soil or by rotting of crop refuse. Composting will kill most plant pathogens if the compost heats properly and the temperature is maintained long enough. The compost pile must have a minimum volume of one cubic yard and be turned frequently to kill pathogens in the plant refuse. Turn the pile every two or three days to provide aeration and mixing. Adding sawdust, leaves, etc. helps to provide a mixture more likely to heat properly. Keep the pile at 65 to 75 percent moisture (fairly moist, but not wet). Add water if necessary to maintain the proper moisture. These procedures help maintain high temperatures. Pathogens are killed if the temperature in the pile is 120-160 degrees Fahrenheit for two to three weeks. Temperatures can be checked with a candy or meat thermometer partially buried in the pile. If the temperature is too low or turning is not frequent enough, some pathogens will survive, particularly those near the edges of the pile. If high pile temperatures cannot be maintained, then plant refuse from fall sanitation might best be destroyed. Flower plants with white mold should also be destroyed rather than composting them. Further information on composting is available in Extension Circular H-885, "Composting Practices."
Fall Application of Lime Sulfur
Lime sulfur can be used in autumn after leaf drop to kill many overwintering fungus disease spores. This is a handy way to reduce overwintering populations of disease organisms and can be done in conjunction with fall sanitation. Use lime sulfur after leaf drop and pruning on rose, raspberry and blackberry canes. Lime sulfur, applied in the fall, will reduce overwintering disease organisms on plum and cherry, including the plum pockets (Figure 5) fungus. Spring application just before bud break may be the most effective time to control plum pockets, but fall application also will help. Lime sulfur can be used on apples to reduce the carry-over of several disease organisms, including powdery mildew. It may also be used on various shrubs such as lilac and alpine currant to reduce the overwintering populations of powdery mildew.
Figure 5. Plum
pockets. Note that the infected fruit is bladder-like and much larger than the healthy
green fruits.For more information consult the following circulars:
- PP454---Diseases of Apples and Other Pome Fruits (1993) .20
- PP469---Plant Disease Management in the Home Garden (1995)
- PP656---Disease Management in Home-Grown Cucumbers, Melons and Squash (1991)
- PP659---Disease Management in Home-Grown Tomatoes (1992)
- PP689---Disease Control in Cherries, Plums and Other Stone Fruits (1991)
- PP697---Deciduous Tree Diseases
- PP789---Diseases of Evergreens and Related Problems
- H885----Composting Practices
- PP899---White Mold of Vegetables and Ornamental (1986)
- PP950---Lawn Diseases (1988) 1.00
Checklist of Fall Activities
Table 1 gives a checklist of fall home garden activities for disease prevention.
Table 1. Home garden fall activities for disease prevention. ------------------------------------------------------------ Plant Activity ------------------------------------------------------------ Apple, crabapple Rake up and destroy leaves Mark fireblight cankers for pruning in early spring. Disinfect pruning tools. Prevent sunscald. Apply lime sulfur after leaf drop. Ash, Oak Rake up and destroy leaves if anthracnose was present. Remove branches with anthracnose cankers. Cherry, Plum Rake up and destroy leaves. Cut out black knot cankers. Remove abnormal fruits clinging to tree. Prevent sunscald. Apply lime sulfur after leaf drop. Corn Destroy smut galls. Remove stalks to prevent carry-over of soil borne stalk rot disease organisms. Cucurbits Remove and destroy unproductive plants. (cucumbers, Destroy all plants and fruits after melons, squash) killing frost. Control cucumber beetle into the fall. Evergreens Water thoroughly (at least 3" of water) before freeze-up. Apply antidesiccant just before freeze-up. Flowers, Remove and destroy dead plants. ornamentals, Take special care with any killed by white perennials mold. Lawns Rake clean and keep mowed. Don't fertilize between mid-July and mid-September. Peony After killing frost, cut off tops at ground level and destroy. Raspberry Prune out diseased canes; remove 2-year-old canes that have borne fruit. Apply lime sulfur to canes (after leaf drop and pruning). Rose Rake up and destroy leaves. Cut out diseased canes. Apply lime sulfur to canes (after leaf drop and pruning). Tomatoes, Remove and destroy all vines, fruits, and Potatoes tubers. Trees Prevent sunscald on trees with thin bark (e.g. mountain ash and silver maple) Vegetable garden After removing all crop refuse, spade or rototill the soil. ------------------------------------------------------------
PP-737 (Revised), January 1987
Reviewed July 1996
