Potato Crop Update - #2, June 10, 2003
	Contents: Crop Growth and Development Update. A.J. Bussan, Vegetable Specialist, UW-Madison, Horticulture Potato Disease Update. W. R. Stevenson, Department of Plant Pathology, UW-Madison
Crop Growth and Development Update Alvin J. Bussan, UW-Madison, Horticulture Department, 608-262-3519 or ajbussan@wisc.edu
Weather has continued to be mild over the past 7 to 10 days which has promoted good crop growth and development. Many irrigation systems were running during the latter part of last week as we went several days with little to no precipitation. A number of growers have been applying fertilizer over the past week and hilling is well under way with some growers already having finished. Almost all the crop should have emerged by now. I have not heard any reports of poor stands suggesting good crop establishment. At the Hancock Station, we have estimated 90+% emergence of the potato crop across 10 to 15 different varieties. One variety has not emerged well and I suspect seed piece decay affected that variety as seed piece remnants were difficult to find in hills with poor emergence. I do not think they were skips as we hand planted the trial. Early canopy development is progressing quickly. We estimated canopy cover at 15 to 45% last Thursday. I heard reports of the crop canopy being 60% closed in early planted Superiors. Canopy development has differed with variety, seeding date, and seed quality in trials at Hancock. Canopy closure will likely occur in 10 to 15 days if current weather conditions persist. Chuck Kostichka and I dug several potato hills last Thursday in a Spudpro trial that was planted on April 20^th at the Hancock Research Station. Every variety had already produced stolons and a number of varieties have already initiated tuber set. Tuber size as of last Thursday ranged from simple swelling at the tip of the stolon to tubers ¼” in diameter. One tuber was already more than a ½” in diameter. Set appeared to be heavy as plants had more than 20 tubers. In general, round white and red varieties were more advanced than russet varieties. Chuck was going to have his crew dig and count stolons/tubers on Monday of this week to get a better feel for set at this point. Tuber set did not occur until after June 15 in 2002 again indicating the crop is about 2 weeks ahead of last years crop. Pday accumulation has ranged from 140 to 180 units since May 15. Potential ET has ranged from 0.05 to 0.18 over the last week depending on the day and location. Conditions have been optimal for early potato growth and the crop has been responding with good growth and development. For updated weather information access the UW/UM extension weather site at http://www.soils.wisc.edu/wimnext/. If you have difficulty accessing weather information or would like daily reports contact me.
Potato Disease Update - W. R. Stevenson, Department of Plant Pathology, UW-Madison, Tel. No. 608-262-6291, Email: wrs@plantpath.wisc.edu
We are now at June 10 and counting. Potatoes are growing rapidly and beginning to close the rows. With dry weather over the past two weeks and some timely rains mixed in, we are still looking at low numbers of severity values. Usually at this stage of the year, we are looking at substantially higher numbers of severity values. In fact, one year ago on June 5, there was a total of 22 severity values, high enough to post spray warnings. I am accustomed in recent years to sending out late blight warnings as soon as I return from an annual fishing trip, usually the first week of June. This year, I returned a week later than normal and am pleased to find such a low number of severity values. That removes a bit of the pressure normally associated with this time of the year. P-Days are accumulating on a normal pace, roughly 50 per week from emergence. As a general precaution, I am suggesting that growers consider spraying the foliage with fungicide just prior to row close to insure coverage of the lowest leaves. These areas of the plant are always difficult to cover, once the canopy closes. I do not see an emergency for late blight or early blight control measures, but we need to be prepared as weather conditions can change rapidly. A current accumulation of P-Days and Severity Values can be checked on our web site at http://www.plantpath.wisc.edu/wivegdis/index.htm. The site is updated every 2-3 days with the most current data from our weather stations at Antigo, Grand Marsh, Plover and Hancock. There are currently no reports of late blight anywhere in the Midwest. Stands in Wisconsin are excellent with very little seedpiece decay. The Wisconsin fields I’ve visited are uniform in height and vigor. All in all, we are off to a good start. In my travels to the Churchill River over the past 10 days, I’ve motored through the Red River Valley and up through Portage La Prairie in Manitoba. Crops look good with adequate, but not excessive moisture. Some of the earliest planted potatoes in Manitoba were just beginning to emerge on May 29. We returned from our fishing location on a different road so I couldn’t see how the Canadian potato crop was progressing. They have some beautiful soils to work with on the Canadian prairie and the acreage seems to be increasing, at least the fields on our itinerary. AJ and I will try to prepare a newsletter once a week for the remainder of the growing season. If you have comments, please let us know. If you have a topic that you would like to see addressed, we are open to your suggestions. We want the newsletter to be useful and to help you be proactive to solving pest and crop problems.

Current P-Day and Severity Value Accumulations for 2003

Location	Calculation Date:	P-Day Total	Severity Value Total
Antigo emerging soon	6/9	0	0
Grand Marsh emerging 5/19	6/9	129	3
Grand Marsh emerging 5/24	6/9	105	3
Grand Marsh emerging 5/28	6/9	83	3
Hancock emerging 5/13	6/9	178	5
Hancock emerging 5/17	6/9	154	5
Hancock emerging 5/25	6/9	107	3
Plover emerging 5/13	6/9	168	2
Plover emerging 5/24	6/9	108	2