There will be a couple of hundred acres of Connecticut-type tobacco grown for cigar wrapper leaf in our area this year.
A major concern regarding this enterprise is that most, if not all, of the recommended varieties, have no black shank resistance.
Dr. Emily Pfeufer, Extension plant pathologist for tobacco, prepared the following comments related to battling this disease and how the resistant varieties have allowed us to reduce concern over the past few years.
Management is dependent on the successful combination of crop rotation, resistant varieties, and soil-directed fungicide applications.
Early season symptoms typically become apparent when knee-high, established plants wilt in the heat of the day and revive overnight. Soon after, plants will become yellow and may fail to recover from wilting.
A dark brown, firm, somewhat constricted lesion will develop at the base of the stalk. Central tissue within affected plant stems may have a disked appearance when split.
Spores splashed from soil sometimes infect lower foliage, progressing to greasy, large, leaf lesions. Black shank often affects swaths of plants down the row and in adjacent rows, but in high-pressure fields losses can approach 100%.
Two races of the black shank pathogen are prevalent in Kentucky; race 0 and race 1. Primary infection sites for P. nicotianae are fine root tips and minor root wounds resulting from growth through the soil as well as cultivation damage.
The pathogen colonizes tobacco roots and progresses up the stem of susceptible varieties, disrupting water movement to aboveground plant parts. When an infected tobacco stem is split open, disking of the pith may be observed. Greasy, large lesions may be present on lower tobacco leaves when the black shank pathogen is splashed from the soil.
Black shank can be well-managed, even in high-pressure fields, by combining crop rotation, resistant varieties, and soil-directed fungicide applications. Since the races of the black shank pathogen prevalent in Kentucky are tobacco-specific, planting tobacco only every third or fourth year reduces the amount of overwintering P. nicotianae available to infect the tobacco.
Corn, small grains, rye, wheat, or other cover crops are good rotational choices. Any field with a chance of having black shank pressure should be planted with a variety with at least moderate resistance to both races 0 and 1.
Soil-directed fungicides are a critical component of black shank management. At a minimum, transplant water-administered fungicides (either Orondis Gold with Ridomil Gold SL, or Ridomil Gold SL) are recommended for any field with a possibility of black shank.
In high-pressure fields, up to two post-transplant fungicide applications may be applied toward tobacco stems, then cultivated into soil. Post-transplant fungicide options, applied at first cultivation and/or layby, are Orondis Gold 200 (if not used at transplant), Ridomil Gold SL, or Presidio. Fungicide applications typically conclude before significant plant loss becomes apparent. Read and follow all fungicide product labels.
Alfalfa Weevil InsectWarmer temperatures will no doubt invite alfalfa feeding to begin. Adult alfalfa weevils are one-eighth to one-fourth inch long, grayish brown to black beetles with a broad dark stripe down the center of the back. Groups of eggs are laid in live and dead alfalfa stems during the fall and spring.
The newly-hatched legless, grub-like larvae are pale yellow. They soon become green with a white stripe down the middle of the back. After feeding for about 4 weeks, the full-grown larvae spin a net-like spherical cocoon near the top of the plant and pupate. The adults emerge within 10 days. After a short feeding period, they leave the field and spend the hot summer months hidden and inactive. The adults fly back to alfalfa in the fall and remain there over the winter.
Alfalfa weevil larvae are the most important pest of the first cutting. They feed at the tip of the stem leaving many small rounded holes. Eventually, all of the leaves at the top of the plant may be destroyed. Heavily infested fields take on a bleached-out appearance.
In addition to reducing yield and quality of the first cutting, the second cutting may be stunted. Larval and adult feeding on the regrowth may set back recovery and development after the first harvest.
Be on the watch for feeding and be prepared to spray or harvest the hay early if needed.