Some fungicides are specific for Rhizoctonia Black Scurf control (Moncoat MZ, Moncut, T-22, and Blocker) as evident by less stem and stolon burn, and little or no development of black scurf on the tuber surface. On a few occasions, and for whatever reason, some tubers escape the treatment and show heavy black scurf. Life is never perfect, at least not at Freeville.

Other treatments offer more broad-spectrum control that includes Rhizoctonia, Silver Scurf, Fusarium Dry Rot (Tops MZ, Maxim MZ, Quadris in furrow, or the new formulation called Amistar), and may offer some affect on Black Dot. The material(s) chosen will depend upon the amount of disease pressure on each farm (was rotation out of potato and tomato for 2 or more years practiced), the quality of seed you plant, soil type, the range of diseases involved (previous history and present), and the end product use, whether it is for fresh market, processing, or for use as seed potatoes. With but few exceptions, we have generally seen a tangible improvement in the harvested product from the field with the use of most seed piece or in-furrow treatments tested, especially if an adequate foliage fungicide program was used during the course of the season.

Remember that seed piece or in-furrow treatments are not a cure all, and are primarily intended for Fusarium dry rot, Rhizoctonia, and silver scurf. If seed is of poor quality to begin with, or is handled or planted improperly, no amount of treatment will bale you out of a bad predicament. Seed treatments will not control current season daughter tuber infections with early blight, late blight, common scab (for the most part), powdery scab, white mold, pink rot, or leak. Some of the later diseases can be mitigated by appropriate canopy sprays, but this will be covered in another article. However, the choice of seed quality you elect to use this season can dramatically influence your outcome at harvest. This is especially true for tubers that have 25-50% of the surface area covered with common scab or silver scurf. This is a sure way of introducing these organisms into your field. In the case of common scab, Streptomyces strains vary in their virulence, and planting scabby tubers can easily reinfest the field with another, more aggressive strain. Studies conducted in Wisconsin (Stevenson et al., 2003) have clearly shown that planting scabby tubers will result in a significantly lower yield of US #1 tubers and a significantly higher level of cull tubers.

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. In general, mancozeb (Dithane, Manzate, and Penncozeb) is helpful for Fusarium seed piece decay and is usually applied as a dust formulation. Whole or cut seed can be dipped into these products at the rate of 1¼ (1.25) lbs per 50 gal. of water. However, 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. If treated seed pieces have to be held before planting, the tubers should be spread out to dry in a cool place to reduce the risk of seed decay, which is the culprit whenever seed retains excessive moisture.

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 good activity against Rhizoctonia, and may also suppress 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 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. Moisture and how the cut seed was handled was again the factor for delayed emergence.

In-Furrow Treatments

There are currently two in-furrow treatments registered in New York (Quadris or the new formulation called Amistar, and Blocker) and one more has a pending registration (Moncut). We first tested Quadris as an in-furrow treatment (active ingredient azoxystrobin) in 2000 and immediately saw its potential for controlling Rhizoctonia and silver scurf. Quadris as a liquid (fl oz) was used at the in-furrow rates range of 0.4, 0.6, and 0.8 fl oz per 1,000 foot of row (corresponding to oz a.i. of 0.10, 0.15 and 0.20, respectively) (6.1, 9.2, and 12.4 fl. oz product/A @ a 34" row spacing). The new dry 80% formulation of Amistar will be used at the in-furrow rates range of 0.125 oz, 0.188 oz, and 0.25 oz per 1,000 foot of row (corresponding to the same oz a.i. as for Quadris), with the product usage/A being 1.90 oz, 2.88 oz, and 3.82 oz product/A @ a 34" row spacing. The rate of product used will depend upon how much disease pressure is expected for a given field and/or potato variety, and whether the crop is grown on mineral or organic soils. Higher rates are generally used for potatoes grown on organic soils. Amistar (formerly Quadris) may also be applied as a banded application to potatoes, but most of our work has been with the in-furrow treatment.

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.

NOTE: We have observed delayed emergence and reduced yields for the variety Chieftain (in 3 trials over 4 years) when Quadris was used at 0.958 fl oz/1000 ft, and even with the new formulation of Amistar used at 0.125 oz/1000 row ft in 2003. Similarly results were noted in Wisconsin when this high rate of Quadris was used on Russet Burbank. In our 2003 trial in addition to Chieftain, we included the varieties Andover, Keuka Gold, Marcy, Pike and Snowden. Of these 5 varieties, Pike also showed an early delay in seed emergence and had reduced marketable yields when Amistar was used.

Seed Treatment Comparisons

Growers now have a choice of materials for 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. Tops MZ, Amistar (Quadris) in-furrow and Maxim MZ), and have provided more consistent results. Other products that are registered in the state but were not specifically mentioned include: Maneb Seed Treatment for Potatoes, Gaucho-MZ Potato Seed Piece Treatment, Tops-MZ-Gaucho, and Evolve Potato Seed-Piece Treatment. Make sure to follow the labeled rates and methods of application to ensure maximum protection with these and other products mentioned.

Table 1. Seed Piece / In-furrow Treatment Comparisons (see footnote)

Trade Name

Chemical

Dist.

Rhiz.

Fus

BD**

SS

Control

--

--

--

--

--

--

Moncut 50W* in-furrow

50% flutolanil

Gowan

+++

--

--

--

Moncoat MZ

1.5% flutolanil 6% mancozeb

UAP

+++

++

--

--

Maxim MZ (40-60% load)

0.5% fludioxonil 9.6% mancozeb

Syngenta

+++

+++

+, suppression

+++

Maxim 4 FS (>95% load)

40.3 % fludioxonil (4 lbs ai)

Syngenta

+++

+++

+, suppression

+++

Tops MZ

2.5% thiophanate-methyl 6% mancozeb

Gustafson

+++

++

--

+ or ++

T-22

1.15% Trichoderma

BioWorks

++

+, suppression

--

--

mancozeb

6-7.5% mancozeb

Several

+, suppression

++

--

--

Amistar in-furrow (Quadris)

1.9-3.8 oz/A, @ 34" row; (0.1-0.20 oz ai) azoxystrobin

Syngenta

+++

--

+, suppression

+++

Blocker in-furrow

38.3% PCNB 5.2-10.4 fl oz

Amvac

+++

--

--

--

* Registration pending for NYS.

** Not currently on label. Abbreviations: Diseases - Rhiz. = Rhizoctonia; Fus = Fusarium; BD = black dot; SS = silver scurf; Disease control rating: +++ = best; ++ = good; + = fair/suppression.