Crop Update
Fumigation Essentials – Part 2

Crop Update
Alternaria pressure is increasing in ginseng gardens. While Alternaria diseases in general can affect healthy plants, they tend to be most severe on older tissues and on weakened plants or plant parts. Frost damage has provided weakened tissue that is more susceptible to Alternaria. The symptoms at this time are mainly confined to the stems. Alternaria lesions tend to be dry and brittle and develop a black sooty appearance once the spores (conidia) develop (Figure 1). Without sporulation the lesions could look similar in appearance to the damage from Botrytis infection on frost damaged tissues. However, Botrytis lesions on the stem are not as dry and brittle, tend to be lighter in colour, and will develop a gray, fuzzy appearance when the spores are produced. 

Since both diseases are present in ginseng gardens, it is very important to maintain protection from both diseases. Bravo is registered for both Alternaria and Botrytis and will provide good protection of both diseases. When Botrytis pressures increase, Elevate should be applied to keep the disease under control. Both Rovral and mancozeb products (e.g. Dithane) are also registered for use on Alternaria and these products should be rotated with Bravo for optimal Alternaria control. 

Four-lined plant bugs are present in high numbers in the landscape (Figure 2). While I have received no reports of damage on ginseng so far this year, be on the lookout for symptoms. The insect can attack all ages of ginseng, but it usually only causes economic damage to seedlings. Damage from four-lined plant bug appears as multiple, small brown windows in the leaves (Figure 3). Pounce is registered for control of four-lined plant bugs in ginseng. Consult the label for rates and application procedures. A trap crop of mint, planted at the end of the garden may be sufficient to lure the insects out of the field under normal population pressures. 

Figure 1. Alternaria on a ginseng stem. 

Figure 2. A four-lined plant bug adult

Figure 3. Damage caused by four-lined plant bug on ginseng. 

Fumigation Essentials – Part 2
Effective fumigation requires both an effective product and appropriate methods of application. Proper application procedures are at least as important as the actually product used. However, it is also important to realize that the different fumigants control or suppress different pests. Last week’s issue contained all of the things to consider for proper fumigation. All fumigants should be applied under the best possible conditions, following the label for proper application procedures in order to provide maximal effectiveness. There are four active ingredients and combinations (under several trade names) registered for use on ginseng: 1,3-dichloropropene (Telone II), 1,3-dichloropropene + chloropicrin (Telone C-17), metam-sodium (Vapam, Vapam HL, Busan 1020, Busan 1236), and dazomet (Basamid). This article will summarize some of the important considerations for proper application of each fumigant and list some of the pests that each product controls according to the label. For all products, it is essential that the label directions are followed exactly for optimal control of soil pests. 

Telone II is a liquid soil fumigant. It is a nematicide and is only registered for control of certain species of nematodes, including lesion and root-knot nematode which are known or suspected of causing damage to ginseng. Application procedures are similar to those of Telone C-17.

Telone C-17 is a liquid soil fungicide and nematicide. It provides control of the nematodes controlled by Telone II but also provides control or suppression of certain soil fungi. It is not labelled for control of weeds in the soil. Telone products do not require the use of a tarp for optimal control of pests, but do require rolling or compaction as a seal. Application depth is important, because shallow application will allow the fumigant to escape too rapidly. 

Vapam and Busan (metam-sodium) provide control of some nematodes, soil fungi and weeds. Weeds controlled include annual grasses, chickweed, dandelion, lambsquarters, pigweed, and many other weed species. These products also suppress perennial weeds such as quackgrass. Fungi controlled include Rhizoctonia, Pythium, Fusarium and Phytophthora. Metam-sodium is a liquid fumigant that must be applied to moist soil, when air temperatures are lower than 32C and winds are light. The surface of the soil must be kept moist during application and for 24 hours afterwards. At a minimum, the soil should be moistened after application to seal the fumes in the soil. Tarping after application improves effectiveness. The tarp should remain on the soil for 48 hours. Follow the label carefully for post-application procedures. 

Basamid (dazomet) is a granular soil fumigant that provides control of unencysted nematodes, soil fungi and most germinating weed seeds. Basamid must be thoroughly and evenly cultivated into the soil after application using a rotary cultivator or rototiller. The soil should be suitable for seed germination for 5-7 days prior to application. Tarping will improve effectiveness of Basamid but rolling or flooding the surface can also be used to seal the fumigant into the soil. The soil can be opened up 5-7 days after Basamid application at warm (<18C) soil temperatures. 

In addition to some specific application procedures for each product, all of the registered fumigants have the following requirements for proper use:

1. Soil organic matter must be decomposed prior to fumigation or pathogens could survive in clumps of intact organic tissues.        
2. The better the seal, the more effective the fumigation.         
3. The fumigant must be allowed to dissipate before seeding.        
4. Un-fumigated soil must not be mixed in with treated soil when forming ginseng beds. 

The amount of control or suppression of specific plant pathogenic fungi in the soil by each soil fumigant has not been extensively studied on ginseng. Some soil fungi produce survival structures that are known to be resistant to all of the fumigants. Talk to your chemical company representative for their experience with the product and the specific fungi that may be controlled or suppressed. 

Questions about ginseng can be directed to Sean Westerveld, OMAFRA’s Ginseng and Medicinal Herbs Specialist at 519-426-4323; E-mail: sean.westerveld@ontario.ca.