Planting Date Effect typography
On Bulking, Disease typography

NDSU research studying effects on three russet varieties

For as long as many growers can remember, the thinking has been to get your potato seed in the ground as soon as possible in the spring so they have as long a growing season as possible before the fall harvest.

Pretty simple concept, right?

Yes, but research currently taking place at North Dakota State University is trying to either reinforce that thinking or determine if there is a more optimal date for planting potatoes and the effect that date will have on bulking as well as disease control, specifically Verticillium dahliae.

a planted potato cultivar
the same potato cultivar, planted on a different day

These two photos show the same potato cultivar that was planted on a different date. It shows the effect of the planting date and disease on the potato’s growth pattern.

Jed D. Grow, a PhD graduate student researcher from NDSU, talked about NDSU’s current planting date research in a presentation titled “Planting Dates Effect On the Bulking Rates And Verticillium Content Of Three Russet Cultivars,” which he made at last summer’s Potato Association of America annual meeting in Missoula, MT. Grow’s presentation last summer covered research results from the first year of the study—2021—but final results from this past summer’s studies weren’t finalized by the time we went to press with this issue. Grow did offer some preliminary results, however, in updating what he and his research team discovered from the study’s first year.

The Abstract

This comes from Grow’s abstract from his PAA presentation.

“In a short growing season, planting potato seed tubers as early as possible to accumulate more growing degree days can lead to higher yields, however, planting too early can lead to potential injury to the crop resulting in lower yields. Planting date has also been shown to have an effect on Verticillium accumulation but appears to be cultivar specific. Russet Burbank, Bannock Russet and Dakota Russet were planted at an early, average and late planting dates in Larimore, ND, and Perham, MN.”

The method of how the potato varieties were planted and studied was also explained. “Starting at tuber initiation, subplots of 5 row feet (five plants) were sampled on a two week interval, collecting tubers and stems. Tubers were weighed individually and photographed for vascular discoloration. Stems collected from the five plants were dried and assessed for Verticillium.”

The three russet varieties chosen were done so because of their processing characteristics. The Red River Valley is known for its processing potatoes, which is where a good portion of potatoes go.

Tubers Are The Sink
Grow explained that the period of time between initiation and tuber maturity is when “your tubers are the sink.” He said, “You’re bulking rate is tied very closely—and several studies have been done on this—to the photosynthetic activity of the plant and that correlates strongly with the amount of solids that are being transported and being deposited into your tubers.”

Ideally, he said, “It’s best to at this time to avoid any and all stress. Keep those tubers happy. Keep pests off them.” Of course, heat stress and water stress affect tuber bulking during these periods. While controlling heat stress is difficult, making sure potatoes have enough moisture is much more doable, especially in areas where irrigation water is readily available.

All those factors are important during the growing season but equally important is the timing of getting potato seed in the ground. Grow pointed out, “Planting date affects your overall yield mainly by affecting the length of the growing season.”

He continued, “We are not so blessed with a long growing season in the Red River Valley and so when you’re talking about your overall yield, the number of tubers or your size profile, a lot depends on your planting date.”

Of course, planting too early can be dangerous to your crop as well and there are several factors to consider. “Mainly the things you would want to consider are the soil temperature; what you’re planting into to avoid injury and when you can actually get into the field.” If it’s too wet growers can’t actually work the field but, as Grow pointed out, maybe it’s not too wet to get into the field to plant but the soil moisture is still high so then you might have to worry about rot.

researcher Jed Grow takes a smiling selfie in a field of crops topped with purple flowers

North Dakota State University PhD graduate student researcher Jed Grow.

Studying Disease

The other part of the study besides looking at tuber bulking was researching Verticillium dahliae, which, he reminded growers, can reduce tuber size and yield, promote premature vine death and affect the tuber quality.

While all those are definitely undesirable results of Verticillium, tuber quality is especially troublesome because, as Grow pointed out, his study focuses on processing tubers and any discoloration is a bad deal.

If that isn’t enough, Miscrosclerotia (the resting structure of a fungus) “can stay on tuber debris, on vine debris in the field or in the soil itself for up to 14 years but it’s also ranged in studies from 7 to 20 years,” Grow said. Of particular concern about this, he explained, is sometimes the longer the tubers stay in the ground, the more opportunity there is to leave/deposit/return Verticillium in the soil. Grow said previous research has shown Verticillium dahliae is lower in later plantings but also lower in earlier plantings so his research is trying to get a better handle on that.

With the goal of studying the effects of planting dates on yield, bulking and Verticillium dahliae on those three russet varieties, Grow and his team planted seed early, on the average planting date for the Red River Valley and then later. On the early date, Grow said, “We tried to get in as soon as we possibly could, planting in cooler soils than most growers would.” In 2021, that planting date was April 22. The second planting was May 7 and the third or late planting May 19.

The first bulking test/dig was July 1. To determine rate of bulking Grow said they took second sampling minus what they got on the first sampling as far as weight went and then divided it by the days after planting.

See Figures 1-6 for the 2021 results.

The Results?

Grow’s abstract provided a summary of the 2021 results.

“Planting date on bulking rate was cultivar dependent. Dakota Russet and Russet Burbank had an increase in overall bulking rate for the second planting date later on in the season, and no difference in final yield between the first or second planting date. Bannock seed tubers planted earlier showed the highest bulking rates and the highest end yields compared to later planting dates. These data suggest that planting Russet Burbank and Dakota Russet cultivars later could lead to higher yields, however, planting Bannock Russet earlier in the season is necessary to allow sufficient time for bulking.”

Grow pointed out that the Dakota Russet could have been harvested earlier because it basically stopped bulking but they waited another month. The downside for a grower waiting would be that it could play a role when it comes to disease.

He said, “If you can harvest the Dakota Russet earlier, say Sept. 9, and not get any additional weight gain as far as tuber growth goes, are you only getting Verticillium past that point? How much Verticillium are you going to add back to the soil and will it offset the yield you may or may not get?”

What About 2022 Results?
Moving on to some preliminary results from this past summer’s (2022) research, Grow’s planting options were affected by the same conditions that growers experienced—a cold, wet spring.

The “early” planting in 2022 was mid-May (compared to April 22 in 2021), which was later than the “latest” planting from 2021. The late planting was near the end of June/early July. “That was much later than most any grower in the region would want to plant due to the improbability of not being able to harvest anything,” Grow said.
He added, “The lateness of the season just heightened and intensified the results from 2021.”

What the NDSU researchers found, again preliminarily, was that the Dakota was still bulked and was dying back in October, ready to go. “That shows that with an earlier planting date there is no need to keep the early bulkers in the ground later,” Grow said. “The Bannock Russet, if it wasn’t planted early enough, wasn’t ready to be harvested at all. And the Russet Burbank was still bulking but you could at least have gotten something.”

The Verticillium results were still coming in when we went to press with this issue.

So while the 2022 planting season was a challenge, Grow said it did provide some important information for growers. He explained, “It’s important to get good and bad year’s data when we can plant way early and when we plant later than we’d like because growers face these odds all the time and we want to accurately give them a good date to help them make good management decisions. If we can have them change the planting date and help predict a better harvest date to help them maximize yield and minimize disease accumulation in the soil no matter if it’s a good or bad year, then we’re doing our jobs.”

Committee members on this research include, in addition to Grow, Dr. Juan Orsorno, Dr. Adam Marx, Dr. Julie Pasche and Dr. Gary Secor.

Russet Burbank Growth and Yield line graph
Russet Burbank Tuber Bulking Rate line graph
Dakota Russet Growth and Yield line graph
Dakota Russet Bulking Rate line graph
Bannock Russet Growth and Yield line graph
Bannock Russet Bulking Rate line graph