Table 1. Clonal lineages of Phytophthora infestans detected in the United States and Canada. US-1, US-6, US-7, and US-8 have been locally predominant, and US-8 has been nationally predominant since 1995 (Adapted from Fry, 1998)

Lineage	MT4	met2	Spec3	Gpi	Pep	Dates4
US-1	A1	S	P(t)	86/100	92/100	? - 1997
US-6	A1	R	P-T	100/100	92/100	1980s-93
US-7	A2	R	P-T	100/111	100/100	1992 - present
US-8	A2	R	P	100/111/122	100/100	1992 - present
US-11	A1	R	(P-T)	100/100/111	100/100	1994-1998
US-17	A1	R	T (p)	100/122	100/100	1996-97, NY
Unknown	A1	R	T	?	?	2000, NY

¹ MT is the mating type (A I or A2).

² met refers to metalaxyl sensitivity: S = sensitive; R= resistant.

³ Spec refers to pathogenic specialization. Some isolates are primarily pathogens of potatoes (P), and others are pathogens of both potatoes and tomatoes (P-T). The US-1 clonal lineage contained a few individuals that were pathogenic on both potatoes and tomatoes, but most were pathogenic mainly on potatoes.

⁴ Dates refers to the time during when these lineages were common. The US-1 clonal lineage seems rare since 1993. The US-6 lineage has declined in frequency since 1993. Lineages US -12, 13 and 14 are not included in the table as they appeared in only 1 field in 1994.

Fungicide Update

Here in New York we are limited in the fungicides that have been registered for late blight control. Previcur Flex (propamocarb, Bayer Crop Science, and previously used in New York as Tattoo C) is registered nationally, and is very close to being registered in New York as a restricted use product. The restricted use requirement is because of ground water concerns, particularly for Long Island. Approval by DEC should occur in a day or two once all of the paper work is complete. Previous work by Bill Fry demonstrated that the combination of propamocarb with chlorothalonil provided good control of late blight when sprays were initiated when 1 to 5% disease was present. The current federal label restricts the application of Previcur Flex to 14 days before harvest for potato. Because of the lateness of the crop, and concerns for tuber blight, I will be asking for an emergency crisis exemption for the use of Gavel 75DF fungicide (zoxamide plus mancozeb; Dow AgroSciences). Gavel 75DF is registered nationally, and is close to be registered in New York (September 19?). Because this product provides excellent tuber blight protection, and according to the federal label, can be used within 3 days of harvest, this additional product will provide needed benefits for the late maturing crop.

In the meantime, use protectant fungicides (chlorothalonil, mancozeb, maneb, metiram and triphenyltin hydroxide) at full-labeled rates and on a 5-day schedule. The quota of the strobilurin fungicides (Quadris and Gem) has probably already been met with previous early blight fungicide sprays, and their use should be limited because of concerns for developing fungicide resistance. Curzate (cymoxanil) plus a protectant fungicide is also registered in New York for late blight control. Previous work from Bill Fry's program has demonstrated that Curzate was not as effective under warm growing conditions.