Wednesday, September 26, 2012

Lawn Pests Can Lead to Hungry Critter Invasion

Suspected skunk damage to lawn due to their feeding on white grubs in the soil

"This looks like predators feeding on the white grubs. Skunks make 2-3 inch diameter holes just through the thatch. A single skunk will make about 100 holes in one night. The raked areas are probably caused by raccoons. They pull back the turf in areas 5 to 18 inches long and about 5-6 inches wide."

"They need to control the white grubs before reseeding or re-sodding because the grubs will kill the new grass. Controlling the white grubs will eliminate the mammal predator problem." - Phil Nixon, U of I Extension Entomologist

Question:  Will the skunks go away after I treat for the grubs?

Answer:  "The skunks have probably been there for years and will continue to be there. They will stop damaging the turf once the grubs are dead. Skunks are usually secretive and nocturnal, so most people don’t see them. Skunks are probably in almost every residential neighborhood in the U.S., along with rabbits, raccoons, and frequently coyotes. Residential neighborhoods provide more diversity of harborage and food than most natural areas, so wildlife numbers in them has been higher than in more rural areas since the 1960’s." - Phil Nixon, U of I Extension Entomologist

Suspected bird damage to lawn due to their feeding on white grubs in the soil

"This photo looks like bird damage. Insectivorous birds such as starlings, blackbirds, robins, cowbirds, and cuckoos will chicken-scratch the turf away to get to the grubs. " - Phil Nixon, U of I Extension Entomologist

Wednesday, September 19, 2012

Soybean Stress Disease

This is one of the many soybean samples that we have started to receive late in the season.  As always, we evaluate the plants for disease.  What do we know about this field?  This is the second time in a row that it has been planted to soybeans and it was previously pasture ground before that.  There has been no soil test done to evaluate fertility.  Most of the field is having problems, which leads me to believe that the main problem is not a disease.

There were several plants that appeared to have insect injury on the stems and pods.  It is difficult to know what type of insect fed on the plants without seeing the actual insect; however we suspect that it may have been bean leaf beetles. 

The stems of all the plants were split and a few of the plants consisted of a dark pith.  This area was cultured to determine what was causing this darkening of the inner stem.  Sometimes we isolate various pathogens, but in this case, we isolated a fusarium sp. and this points to Fusarium blight or wilt. The following is information about this disease was taken from the Compendium of Soybean Diseases:  Symptoms of this disease will appear midseason during hot weather, particularly on plants growing in sandy soils.  This disease has not been reported in seedlings.  The most characteristic symptoms is a black or brown of vascular system in roots and stems, which is evident when stems are split.  Leaves of affected plants may become chlorotic, wither, and eventually drop.  Flaccid leaves and wilting of stem tips are most common on young plants.  Pods of infected plants are often poorly developed, but root rot is minor.  If available, cultivars with resistance to Fusarium and soybean cyst nematodes should be grown.  High quality seeds should be planted in warm, well-drained soil, and cultivation practices that prevent or reduce soil compaction and promote favorable soil moisture should be used.  Good soil fertility should be maintained.  Crop rotation with non-hosts may reduce inoculum levels.

The roots of the soybeans were examined and found to be somewhat infected with Rhizoctonia sp. The Compendium of Soybean diseases states that as the season progresses, root symptoms can be found on the plants at the advanced vegetative to reproductive growth stages.  These plants may have been infected as seedlings and have lesions that are enlarging to girdle the stems (as seen on this sample).  Infected plants can be stunted, yellow, and have poor root systems because lateral roots often decay, leaving only the taproot and secondary roots.  Wilt symptoms associated with root rot occur throughout the early reproductive stages, when the disease occurs with warm, dry weather, herbicide injury, soybean cyst nematode damage, and other stresses.  Diseased plants first appear in areas where water and nutrients are poor, such as on hillsides, and may be scattered in lightly infested fields or in circular, discolored areas in heavily infested fields.  Disease patches are sometime elongated, following the direction of tillage.  There is no resistance available for R. solani in soybeans.  Good cultural practices promote seedling health during early stages.  Other stresses, such as herbicide injury, poor soil, insect damage, and feeding by SCN should be reduced.

Can we blame this field's problems on disease?  The answer is no. I am sure some of the blame can be put on the hot and dry weather, but further investigation will need to be done to find out if other stresses could be causing these soybeans to be more vulnerable to these diseases.

Thursday, September 13, 2012

Pepper -Which came first? Sunscald or Alternaria infection?

Alternaria sp. fungus that has infected a bell pepper with suncald.

This bell pepper sample had a round, necrotic area with black fungal growth, on the surface of the fruit. Based on the symptoms of the sample, it appeared to be sunscald, an environmental problem. This problem arises when the pepper is exposed to high levels of sunlight under high temperatures. The dead tissues are only present on the side of the fruit that is exposed to sunlight.

In addition, this sample appeared to have a black fungal growth, covering the sunscald area.  This is an Alternaria sp. (a fungus pathogen) that can invade the damaged tissues (from sunscald or other issues) on the fruit and can continue to cause injury. 

Alternaria sp. is controlled by avoiding conditions that predispose peppers to infection.  There are no approved fungicides or biocontrol agents known for postharvest application to pepper fruit.  If possible, planting should be scheduled so that harvest does not occur during very hot or cold weather, or drought.  Grow pepper cultivars that provide good shading of fruit and be sure that the fertilization includes adequate calcium.

Bell pepper with sunscald.
Certain varieties of the peppers can be more sensitive to sunscald. In lieu of the recent high temperatures and sunlight, it is recommended to plant varieties of peppers that are more tolerant towards the condition.  For example, if you continue to have problems with sunscald, you may try to grow another pepper variety. You can also try to encourage more of a canopy to shade the peppers from the sun (culturally as well as adding fertilizer (N).

Thursday, September 6, 2012

Pythium Damping-off at the Soil line of Cucumber

Pictures courtesy of Mike Roegge

Pictures courtesy of Mike Roegge

Pictures courtesy of Mike Roegge

No greenhouse operation is immune from possible disease problems.  The U of I Plant Clinic received this cucumber sample from a greenhouse that was growing cucumbers in a soil-less medium.  The symptoms were rotting in the lower part of the stem, near the soil line, of most of their cucumber crop.

The rotted tissue at the soil line was examined under the microscope at the U of I Plant Clinic and many oospores were found embedded within that tissue.  The symptoms, along with the presence of oospores embedded within the diseased plant tissue, is most likely due to pythium damping off at the soil line.

Oospores seen within the rotted tissue under the microscope
Plants will develop a watery rot in the taproot and hypocotyl at or near the soil  line.  Decline, necrosis, or sudden wilt (collapse during the heat of the day) are some symptoms that can occur after infection takes place.  Several species of Pythium can be involved.  Conditions favorable for disease development can differ depending on the pathogen species, but most likely cool and wet conditions are favorable for disease infection.

I consulted with Dr. Babadoost, U of I Extension Fruit and Vegetable Plant Pathology Specialist, to provide possible management solutions for this disease in this particular greenhouse operation.  He recommended that first and foremost, that they cut back on watering these plants as much as possible.  In addition, they may want to increase the temperature in the greenhouse, if possible.  As always, sanitation is very important.  They will not be able to save the infected plants, but to provide protection for unaffected or future cucumber plantings, they may want to apply Phosphite products or metalaxyl (Apron, Ridomil, Subdue) fungicides.