Even though much of New Jersey has had wet weather recently, which is more favorable to Pythium and Phytophthora development, Rhizoctonia root rot has been reported over the past few weeks in a number of crops. Rhizoctonia root rot, caused by Rhizoctonia solani, is an important soil-borne fungal pathogen with a very large host range. The pathogen can survive saprophytically on living or dead plant material (organic matter) or as sclerotia in the soil (for more than 3 years). Disease development is favored by warm temperatures, dry (or very well drained) soils and stressed plants. Symptoms of Rhizoctonia root rot may begin as stunted plant growth (with poor root systems) with the appearance of brown lesions at the base of the stem causing wilting with lesions eventually girdling the stem and killing the infected plant. Rhizoctonia root rot infections only extend about an inch above the soil surface (Figure 1), unlike Phytophthora blight infection which can extend much farther up the stem. [Read more…]
Diagnosing Collar Rot and Alternaria Stem Rot of Tomato
Collar rot (Alternaria linariae) or Alternaria stem rot (Alternaria alternata f. sp. lycopersici) of tomato are common in young tomato plants. Either can be particularly troublesome in seedlings that have been held in transplant flats for an extended period of time before transplanting in hot, humid greenhouses. Collar rot infections often start where a leaflet branch has been broken or pruned which allows a point of infection. Symptoms of Alternaria stem rot include brown circular to irregular lesions on stems with definitive concentric black rings (very similar to Early blight on infected leaves). Symptoms of Collar rot are similar and may or may not produce concentric black rings. Infections that start in the greenhouse may lead to losses in the field as stems become girdled causing the plant or branches to wilt and die. Most commercial tomato varieties have resistance to Alternaria stem rot. While resistance is lacking to Collar rot, growers should chose varieties with Early blight resistance. Fungicides used to control Early blight are also effective against Collar rot.
Symptoms of Collar rot in young tomato |
Allium leaf miner update: 04/29/24
Allium Leaf Miner (ALM)
As of last week, allium leaf miner (ALM) adults were still being captured on sticky cards placed in chive plantings in Mercer and Hunterdon counties, and in a garlic planting in Morris County. Numbers had declined somewhat from catches the week of 4/15. There is a possibility that damaging levels of ALM adults remain. Once we cease to capture adults, another update will follow.
Photo: Sabrina Tirpak. Allium leaf miner oviposition scars on onion
Growers should consider initiating the control method of their choice at this time, if any allium crops are in the field. Affected crops include chives, scallions, garlic, onions and leeks. Look for neat rows of white spots descending from the upper tips of allium leaves (see photo at left). Initial injury often occurs on the tallest leaves. Under warmer, less breezy conditions, adults may be seen near the tips of leaves (see photo of adult at lower right). Perennial chive beds are often the first, and most heavily infested alliums of the spring season, so this makes chives an ideal crop to confirm ALM adult activity.
Floating row covers, kept on until this flight ends will help minimize access to plants. Insecticide applications targeting adults may be helpful as well, although frequency of applications is uncertain. Spinosyn materials (Radiant, Entrust (OMRI approved)), pyrethroids (Mustang Maxx, 
Warrior), neonicotinoids (Scorpion, Venom), the diamide Exirel (section 2ee recommendation) and the insect growth regulator Trigard are labeled for miner control.
Allium leaf miner update: 03/25/24
Allium Leaf Miner (ALM)
Many weather stations on the NEWA network except for typical colder sites in northern New Jersey have surpassed 250 growing degree days (GDD) base 39˚F. 39˚F is close to the lower developmental temperature (38.3˚ F) which our colleagues at Penn State recommend for predicting the first emergence of ALM adults. In recent years, initial feeding/egg laying scars have been detected within a few days of local weather stations recording the 250 GDD threshold. Growers who feel they may be impacted by this pest should check the accumulated GDD from local weather stations. Growers in southern counties may reasonably assume there will be ALM activity in their area soon, if not already happening. To determine GDD from local weather stations, the NEWA website https://newa.cornell.edu/ is very helpful. From the NEWA home screen, select the nearest weather station from drop down menu at the center of the page. Next, scroll down to “Weather Tools” on the right side of the page, and select “DD Calculator”. Select your start date (1/01/24) and end date as well as Degree Day Type (39 F) from the menu at the left of the page. The site will automatically generate the accumulated GDD base 39F to the last day of your requested sample, and then offer a forecast of accumulated GDD for the next week. If you should select 1˚C, then the DD accumulation should be 350.
Photo: Sabrina Tirpak. Allium leaf miner oviposition scars on onion
Growers should consider initiating the control method of their choice at this time, if any allium crops are in the field. Affected crops include chives, scallions, garlic, onions and leeks. Look for neat rows of white spots descending from the upper tips of allium leaves (see photo at left). Initial injury often occurs on the tallest leaves. Under warmer, less breezy conditions, adults may be seen near the tips of leaves (see photo of adult at lower right). Perennial chive beds are often the first, and most heavily infested alliums of the spring season, so this makes chives an ideal crop to confirm ALM adult activity.
Floating row covers, kept on until this flight ends will help minimize access to plants. Insecticide applications targeting adults may be helpful as well, although frequency of applications is uncertain. Spinosyn materials (Radiant, Entrust (OMRI approved)), pyrethroids (Mustang Maxx, Warrior), neonicotinoids (Scorpion, Venom), the diamide Exirel (section 2ee recommendation) and the insect growth regulator Trigard are labeled for miner control.
Adult activity and observations of feeding will be reported on in the IPM Update as they occur.
Understanding and controlling Rhizoctonia root rot
Even though much of New Jersey has had wet weather recently, which is more favorable to Pythium and Phytophthora development, Rhizoctonia root rot has been reported over the past few weeks in a number of crops. Rhizoctonia root rot, caused by Rhizoctonia solani, is an important soil-borne fungal pathogen with a very large host range. The pathogen can survive saprophytically on living or dead plant material (organic matter) or as sclerotia in the soil (for more than 3 years). Disease development is favored by warm temperatures, dry (or very well drained) soils and stressed plants. Symptoms of Rhizoctonia root rot may begin as stunted plant growth (with poor root systems) with the appearance of brown lesions at the base of the stem causing wilting with lesions eventually girdling the stem and killing the infected plant. Rhizoctonia root rot infections only extend about an inch above the soil surface (Figure 1), unlike Phytophthora blight infection which can extend much farther up the stem. [Read more…]
Diagnosing Southern blight and White mold in tomato and pepper
There have been a few reports of Southern blight (Sclerotinia rolfsii) and White mold (Sclerotinia sclerotiorum) on tomato and pepper in New Jersey. Southern blight is much more common in vegetable areas south of the state where summer temperatures remain hotter (above 90°F) for longer periods of time. Like white mold, it can survive in the soil for many years. Symptoms of Southern blight include infection at the base of the stem at the soil line. The resulting infection will girdle the plant causing wilt and death. The fungus will produce white, cottony mycelium and very small, spherical sclerotia which are often have a tannish, brown color.
White mold is more common than Southern blight in New Jersey, and like Southern blight, once introduced into a field or high tunnel it can very difficult to control. The pathogen produces large black sclerotia on the surface and inside infected stems. If sclerotia of either pathogen make their way back into the soil, both can survive for years causing significant problems.
All infected plants need to be removed immediately and disposed of properly to help reduce the chances of sclerotia returning to the soil.
For more information on chemical control please see the 2022/2023 mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Symptoms of Southern blight on infected pepper plant. Note the numerous, small white to tan colored sclerotia on the stem.
White mold of tomato. Note the large black sclerotia developing inside the brittle stems.
