ISSUE 2 May 9, 2002
CERTIFIED SEED IS FIRST LINE OF DEFENSE AGAINST ANTHRACNOSE OF DRY BEANS
With a limited supply of dry bean seed available this year, some growers may be tempted to plant bin-run seed in their fields. Planting bin-run seed poses a risk of introducing the fungal pathogen that causes anthracnose (Colletotrichum lindemuthianum) into a field previously free of the pathogen. With favorable environmental conditions, this introduction could lead to a severe disease outbreak. Even if bin-run seed is treated with a fungicide, anthracnose could still be introduced to a field. This is possible because the pathogen may be beneath the seed coat, where it would likely not come in contact with the fungicide. Seeds that have been infected with anthracnose may not show symptoms or be discolored, so even visually "healthy" bin-run seed may harbor the pathogen. Anthracnose on dry beans is a new disease to North Dakota, and occurred in a few commercial fields located in Pembina, Steele, and Towner counties in 2001. It is crucial that certified anthracnose-free seed is planted, so that this disease will not be introduced to any new fields.
SECTION 24C LABEL FOR EQUUS DF APPROVED FOR CHICKPEAS
A state local needs label (24c) has been granted for the use of Equus DF (chorothalonil, Griffin L.L.C.) on chickpeas to control Ascochyta blight prior to the flowering stage. The labeled rate is 1.25 to 1.8 lbs/acre, with a maximum of 5 applications in a season, as long as no more than a total of 7.2 lbs/acre is applied in a season. Application should begin at the first onset of disease, which may occur 2 to 4 weeks before flowering.
Extension Plant Pathologist
WHEAT EMERGENCE, COLD SOILS, AND SEEDLING BLIGHTS
Cold soils and injury to sprouted grain: With soil temperatures remaining cool, many growers are still wondering when their planted wheat will emerge and if cold soil temperatures have caused seedling death or decay. Wheat roots and coleoptiles should be able to withstand temperatures down to about 19-210F for moderate durations. Soil temperatures, measured at the 4" depth by NDAWN stations, have NOT dipped below the mid-thirties the last few weeks, and are averaging in the low 40s, so sprouted grain should still be safe from cold temperature injury.
Cold soils and seedling blight: Prolonged exposure to cool wet soils may lead to seed and seedling rots. However, soil temperatures have been too cold for most soil fungi that cause root rot. Even Pythium fungi, which like cool, wet soils, do their greatest damage to wheat between soil temperatures of 59-680F.
Only a few locations in the SE portion of ND have seen soil temperatures in the high 50s so far, and those were for short duration. Seed planted very recently or in the near future may be at greater risk of seed rot or seedling blight when soil temperatures consistently get into the 50s. Thus, late seeded grain should still be treated with a fungicide seed treatment.
PREDICTING WHEAT EMERGENCE
Accumulated Growing-degree days (AGDD) may be used to predict spring wheat growth stages. Accumulated GDD relates plant development rate to air temperature. For spring wheat, the base temperature used for calculations is 320F. An accumulation of approximately 180 GDD after planting are needed for wheat to emerge (Bauer, A. et al. 1984. Use of growing degree days to determine spring wheat growth stages, NDSU Extension Circular EB-37).
NDAWN weather data indicates that accumulated GDD from April 1 - May 7 varies from a high of around 420 at Wyndmere in the SE to lows of 289 at Bowbells in the NW and 293 at Langdon in the NE. Subtracting 180 GDD from these totals and looking at the NDAWN tables indicates that wheat would have had to be planted by around April 12-16 for emergence to be visible by May 7th, with the earlier seedling dates required in the north. Actual emergence dates may vary slightly because the wheat GDD model of Bauer’s is based on air temperatures, and the recent cold soil temperatures may alter this model slightly.
Information about current accumulated GDD at various NDAWN sites across the state may be found at the following web site:
Extension Plant Pathologist
NDSU PLANT PEST DIAGNOSTIC LAB
The recent down turn in temperatures is not making for a pleasant and promising spring! It also presents challenges for those plants that have already emerged or for some greenhouses. There have been some calls to the lab regarding red or purple coloring on foliage of greenhouse tomatoes, and tulips planted in beds next to a house. These color changes in the foliage should be transient and are likely the result of the cool to cold temperatures. Under stress, plants produce reddish or purple pigments called anthocyanins. These are transient in response to the stress, and in this case, should disappear when temperatures warm up.
Cheryl Biller, Diagnostician