Earwigs, Squash Bug, Onion Thrips
August 3, 2011
In this Issue:
Tomato russet mite is a tiny mite that feeds on the undersides of leaves. It is not visible to the naked eye, so therefore the damage might be misdiagnosed as a disease. The lowest leaves will show symptoms first, and in heavy populations, the entire plant will be affected.
Feeding causes leaves to turn yellow, curl upwards, dry out and drop. The stems and leaves also appear bronzed and the leaves will feel greasy. Injury resembles nutritional deficiencies, plant disease or water stress.
Treatment: Cover the tops and bottoms of leaves, and spray when temps are below 85F. wettable sulfur (Grants) (+ spreader-sticker); horticultural oil; abamectin (Agri-mek)
|Verticillium wilt of potato|
|Verticillium wilt of zucchini|
Tomatoes and potatoes can sometimes be affected by soilborne pathogens such as verticillium or fusarium. These are two different fungi that harm plants in different ways, but the symptoms are similar. Leaves turn yellow and dry, often without wilting. Symptoms appear on oldest leaves first, and later move to younger leaves. Leaves turn yellow and then brown on the edges, or entire leaves die. In other cases, shoot tips or the entire plant may wilt slightly during the day and recover at night. As leaves are lost, the remaining leaves will curl upward but remain alive.
Fungi that cause verticillium and fusarium live in the soil on tiny debris particles where they can persist many years. Fusarium kills the roots and phloem, and verticillium clogs the water-conducting vessels (xylem). Eggplants, peppers, and many cucurbits can also be affected.
If you suspect verticillium wilt, cut the plant off at the soil line and looking at a longitudinal section of the cut end. There will be a light tan discoloration of the vascular tissue that occurs inside the stem, running just below and just above ground level. Infected potato tubers may also show tan or blackened discoloration, occurring in rings, especially near the stem end. Infected tubers are safe to eat.
Treatment: The first step is to get a positive diagnosis at the Utah Plant Pest Diagnostic Lab. Other diseases or even drought stress can cause similar symptoms. There are no fungicides for verticillium or fusarium; the best option is to remove infested plants and keep the remaining plants health with optimal watering. At the end of the season, remove all plant and root material out of the infested area. Rotate to resistant crops for at least 3 seasons, then, use resistant cultivars. Fusarium is worse in overly wet soil, so be sure to only water when necessary.
We’ve had a few reports of tomatoes with leaf spotting and yellowing foliage. There are a number of causes for symptoms like these, and one is a fungal disease called early blight, caused by the fungus Alternaria solani. Older leaves will be most affected, with circular spots containing concentric rings like a target. Usually spots will have a yellow halo. Fruit lesions occur at the stem end and are brownish black.
It overwinters on old plant debris and can be a problem where tomatoes and/or potatoes are planted in the same location in successive years.
Warm, rainy conditions are optimal for infection, as is using overhead irrigation. Monitor plants for these distinctive lesions and apply a fungicide as a preventive (to protect the uninfected foliage) as necessary. This fall, till or remove all plant residue in infested fields and next season, rotate out of tomatoes and potatoes for 3-4 seasons.
Treatment: Spray fungicide every 7-14 days until wet weather dissipates; fixed copper (Bordeaux, NuCop, Cuprofix, Kocide), maneb, chlorothalonil, trifloxystrobin (Flint)
|Cercospora leaf spot of eggplant|
|Bacterial leaf spot of tomato|
Cercospora and alternaria leaf spots are common fungal-caused leaf spots on eggplant. Neither species affects the fruit. They overwinter on plant debris in the soil, and usually affect the older, lowest leaves first. If leaves are kept dry infections will not spread, but with multiple overhead waterings, the disease can become severe, causing loss of foliage and a reduction in yield.
Pseudomonas is a bacterium that causes leaf spots on pepper, tomato, cucumber, and other vegetables. It is active during warm, wet weather.
Treatment: To prevent leaf spots in successive seasons, remove all plant debris after harvest, make sure seeds or new transplants are disease-free, and rotate crops. Fungicides should not be necessary on light infections. Severe cases may warrant regular preventive sprays of a fungicide (C-O-C-S, Kocide, Champ, Maneb).
If you are noticing entire canes wilting in your raspberry field, or canes with scorched or curled leaves, it is possibly damage from the raspberry crown borer. Larvae are actively feeding in the roots and crowns now, and entire canes can be killed in response to the feeding. Often, the canes can be easily pulled out of the ground. You may see some tunneling in the lower part of the cane.
The crown borer is a clearwing moth, and the larvae live and bore into the crown and roots of blackberries, raspberries, loganberries, and wild brambles. The problem with this pest is that low levels of infestation can suddenly develop into a severe problem, so it is important to keep an eye on the health of your plants during the entire season.
The crown borer larvae actually spend two years feeding and developing in the plant, and the damage is most evident during the second year of larval activity. Early in their life cycle, they are feeding on the smaller roots, and as they get larger, they move to the crown. Pupation occurs in the crown in mid to late August.
Treatment: Early fall is the best time for treatment because at that time, larvae leave the crowns and move to the roots for the winter. Drench roots once with a product containing bifenthrin in early fall. At least two years of diligent treatment is necessary in an infested patch or field.
Precautionary Statement: Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed herein.