Seed Piece Treatments

            Time was when growers only thought of using captan or mancozeb as the principal seed-dusting agent. Today mancozeb (abbreviated as MZ) is still used alone or in combination with other fungicides to extend the range of pathogens controlled. Mancozeb (Dithane, Manzate, Penncozeb) is helpful for Fusarium seed piece decay. Most of our experience has been with mancozeb applied as a dust. Recently, treatment of whole or cut seed by dipping at the rate of 1¼ (1.25) lbs per 50 gal. of water has been suggested. On a precautionary note, research done at Penn State showed a reduction in yield of US #1 Superior potatoes when tubers were dipped into mancozeb. Moist is never a friend of tubers, so if treated seed pieces have to be held before planting, the tubers should be spread out to thoroughly dry in a cool place to reduce the risk of seed decay.

            With Rhizoctonia being a major concern, growers now have the option to select between several seed piece products. Moncoat MZ with the active ingredient flutolanil is very active for Rhizoctonia and provides safe control of Fusarium. The biological agent T-22 Planter Box (Trichoderma harzianum) has activity against Rhizoctonia, while suppressing Pythium and Fusarium. Two additional products that extend the range of pathogens controlled are Tops MZ and Maxim MZ. Tops MZ relies upon the activity of thiophanate methyl plus mancozeb to provide activity against Rhizoctonia, Fusarium, and silver scurf (Helminthosporium solani). This product has not performed as well as others for daughter tuber protection against silver scurf and black dot (Colletrotrichum coccodes) in tests conducted at Freeville. On the other hand, Maxim MZ (active ingredient fludioxonil with mancozeb) has provided consistent control of Rhizoctonia, Fusarium, and silver scurf. We have not tested the liquid formulation known as Maxim 4FS, but results from Wisconsin did show significant reduction in emergence and yield of US#1 Russet Burbank. These studies compared of effects of Maxim 4FS + Alder Bark, Maxim DP, and Maxim 4FS + Fir Bark on cut and healed tubers vs. freshly cut tubers. Seed decay occurred when Maxim 4FS + Alder Bark and Maxim DP was used on the freshly cut tubers, but not with the other treatments. Holding the cut seed for 6 days significantly reduced the amount of seed decay regardless of the treatment. Alder bark is responsible for keeping a very moist condition that resulted in seed piece decay.

In-Furrow Treatments

            There are currently two in-furrow treatments registered in New York and one more is pending registration. Quadris in-furrow (active ingredient azoxystrobin) has shown excellent activity against Rhizoctonia, silver scurf and black dot, and has been widely adapted for use upstate and on Long Island. Apply Quadris at the in-furrow rates of 0.4 – 0.8 fl oz per 1,000 foot of row. We have noted delayed emergence and reduced yields of Chieftain when Quadris was used at 0.958 fl oz/1000 ft. Similarly results were noted in Wisconsin when this high rate was used on Russet Burbank. Block 4F (active ingredient pentachloronitrobenzene, PCNB) as an in-furrow treatment provides excellent control of Rhizoctonia. We have also tested Moncut in-furrow (active ingredient flutolanil), and achieved excellent Rhizoctonia control. This product is currently not labeled in the state.

Seed Treatment Comparisons

            Growers now have a large range of materials as potato seed treatments (Table 1). All of the materials tested provided good control of Rhizoctonia, whether applied as a seed treatment or applied in-furrow. However, some products extend the range of pathogens controlled (ie. Quadris in-furrow and Maxim MZ), and have provided more consistent results. Make sure to follow the labeled rates and methods of application to ensure maximum protection with these and the other products mentioned.

Table 1. Seed Piece / In-furrow Treatment Comparisons

* Registration pending for NYS.

** Not currently on label. Abbreviations are: Rhiz. = Rhizoctonia; Fus = Fusarium; BD = black dot; SS = silver scurf.