Yi Wang, Associate Professor & Extension Potato and Vegetable Production Specialist, UW-Madison, Dept. of Plant and Agroecosystem Sciences, 608-265-4781, Email: wang52@wisc.edu.
So far we have about 50% canopy cover on Russet Burbank potatoes (the six rows on the upper part of the aerial image), and the plants have started tuber initiation. This year I noted inconsistent emergence on some of the varieties that we included in our variety/nitrogen trial. We suspected the seeds might have some aging-related issues that impacted the emergence rate.
Physiological aging is influenced by two factors, genetics and environmental stresses. Since potatoes are grown from mother tuber, genetics is at the level of cultivars. Plants that die prematurely often have aged tubers. Late-season high soil temperature may stimulate premature sprouting in the field. However, the main cause of seed tuber aging is the temperature during storage. Higher storage temperatures are usually associated with greater aging (Figure below).
Dormancy is a period during which sprouting will not occur even under optimal conditions. Toward the end of the growing season, abscisic acid (ABA), a sprout inhibitor, is produced by the vine and transported into the tubers. Dormancy is broken when the amount of abscisic acid in the tuber eyes decreases through metabolic breakdown to a level that allows the eyes to respond to conditions favoring sprouting. Young seed is characterized by one dominant eye that suppresses the sprouting of the other eyes (this physiological phenomenon is termed “apical dominance”). Older seed tubers (aged seed) are characterized by the loss of apical dominance among eyes.
Since the major factor in storage that accelerates tuber aging is temperature, people can manage to produce a desired tuber age at planting. Planting older seed of cultivars that tend to oversize such as ‘Yukon Gold’ may have advantages. It may improve uniformity and increase the number of marketable-sized tubers, especially for early markets. This may also be true for seed production in which a smaller tuber size profile might be preferred. Some cultivars such as ‘Russet Norkotah’ do not benefit from aging while others such as ‘Yukon Gold’ and ‘Portage Russet’ might, due to their tendency to oversize for their markets. Note that cultivars differ in the extent of their responses to aging.
To age seed, store it at 38°F, then before planting store for two to six weeks at 55–60°F. To hold young seed, store at 38°F and warm to 45°F just before cutting. Plant in soil that has about the same temperature as the tubers. Cutting tubers breaks apical dominance between eyes, thus releasing eyes to sprout. Because of this, sprout removal may result in more stems and smaller tubers.
Physiologically older aged seed emerges earlier, grows faster, yields higher early, and yields less later than physiologically young unaged seed. Because young seed emerges slower, there is a greater chance of seed decay and cankers (stem and stolon). Do not plant seeds right out of cold storage into soil as this will promote condensation of moisture on the seeds and promote decay. Planting young seeds in warmer soil can hasten its sprout emergence and growth. Warm seeds to 50–60°F for a few days and plant in soil slightly cooler. This will add some physiological age to the seed tuber or pieces. Seeds planted in sandy soil that warms rapidly tends to produce more stems and set more tubers. The result is smaller harvested tubers. Extra nitrogen starter fertilizer can partially overcome the effects associated with aging, as N can partially mimic young seed characteristics. Please note that later planting also tends to produce more stems per plant and lower final yield at harvest.
Amanda Gevens, Chair, Professor & Extension Vegetable Pathologist, UW-Madison, Dept. of Plant Pathology, 608-575-3029, gevens@wisc.edu, Lab Website: https://vegpath.plantpath.wisc.edu/
Current P-Day (Early Blight) and Disease Severity Value (Late Blight) Accumulations will be posted at our website and available in the weekly newsletters. Thanks to Ben Bradford, UW-Madison Entomology for supporting this effort and providing a summary reference table: https://agweather.cals.wisc.edu/thermal-models/potato. A Potato Physiological Day or P-Day value of ≥300 indicates the threshold for early blight risk and triggers preventative fungicide application. A Disease Severity Value or DSV of ≥18 indicates the threshold for late blight risk and triggers preventative fungicide application. Data from the modeling source: https://agweather.cals.wisc.edu/vdifn are used to generate these risk values in the table below. I’ve estimated early, mid-, and late planting dates by region based on communications with stakeholders. These are intended to help in determining optimum times for preventative fungicide applications to limit early and late blight in Wisconsin.
Cumulative late blight disease severity values (DSV) since date:
| Location | May 10 | May 15 | May 20 | May 25 | Last 14 days | Last 7 days |
|---|---|---|---|---|---|---|
| Rhinelander | 10 | 10 | 10 | 7 | 4 | 4 |
| Antigo | 14 | 14 | 14 | 10 | 5 | 5 |
| Plover | 9 | 9 | 9 | 2 | 0 | 0 |
| Hancock | 9 | 9 | 9 | 2 | 0 | 0 |
| Grand Marsh | 8 | 8 | 8 | 1 | 0 | 0 |
| Arlington | 5 | 5 | 5 | 3 | 0 | 0 |
| Spring Green | 9 | 9 | 9 | 4 | 0 | 0 |
Any cumulative values above the preventive action threshold of 18 DSV are highlighted in red.
Cumulative early blight potato physiological days (P-days) since date:
| Location | May 10 | May 15 | May 20 | May 25 | Last 14 days | Last 7 days |
|---|---|---|---|---|---|---|
| Rhinelander | 248.9 | 231.1 | 206.1 | 174.3 | 94.4 | 59.7 |
| Antigo | 251.7 | 232.4 | 207.1 | 176.6 | 98.1 | 61.9 |
| Plover | 292.3 | 265.5 | 233.9 | 197.0 | 109.8 | 61.4 |
| Hancock | 293.4 | 266.1 | 233.2 | 195.1 | 109.2 | 60.6 |
| Grand Marsh | 300.7 | 272.0 | 238.5 | 198.4 | 110.5 | 60.2 |
| Arlington | 313.9 | 283.3 | 246.5 | 204.5 | 113.3 | 58.7 |
| Spring Green | 315.3 | 282.3 | 245.1 | 203.6 | 111.7 | 58.5 |
Any cumulative values above the preventive action threshold of 300 P-days are highlighted in red.
Late blight of potato/tomato. The usablight.org website (https://usablight.org/map/) indicates no reports of late blight from the US so far in 2024. The site is not comprehensive. We accumulated few to no Blitecast Disease Severity Values over the past week in WI.
Early blight of potato. P-Day values will continue to amass (up to ~10 per day) and develop conditions optimum for early blight disease caused by Alternaria solani. Earliest inoculum typically comes from within a field (small crop residue fragments can harbor the pathogen) and from nearby fields. Olee Hoi Lam, a PhD student working with early disease detection in potato with hyperspectral reflectance, is running several Rotorod air samplers in three of our potato research fields at the UW Hancock Agricultural Research Station. On Thursday of this past week, we collected conidia/spores which appear consistent with Alternaria species (pictures of conidia below). Sampling of the air at plant level in these fields will continue on an every-other-day basis. Once established, early blight continues to create new infections due to its polycyclic nature – meaning spores create foliar infection and the resulting lesion on the plant can then produce new spores for ongoing new infections in the field and beyond. Early season management of early blight in potato can mitigate the disease for the rest of the season.
For custom values, please explore the UW Vegetable Disease and Insect Forecasting Network tool for P-Days and DSVs across the state (https://agweather.cals.wisc.edu/vdifn). This tool utilizes NOAA weather data. In using this tool, be sure to enter your model selections and parameters, then hit the blue submit button at the bottom of the parameter boxes. Once thresholds are met for risk of early blight and/or late blight, fungicides are recommended for optimum disease control. Fungicide details can be found in the 2024 Commercial Veg. Production in WI Extension Document A3422: https://learningstore.extension.wisc.edu/products/commercial-vegetable-production-in-wisconsin
Vegetable Insect Update – Russell L. Groves, Professor and Department Chair, UW-Madison, Department of Entomology, 608-262-3229 (office), (608) 698-2434 (cell), e-mail rgroves@wisc.edu. Vegetable Entomology Webpage: https://vegento.russell.wisc.edu/
Potato leafhopper – (https://vegento.russell.wisc.edu/pests/potato-leafhopper/). Last week adult populations of Potato leafhopper (PLH) were increasing in several crops (alfalfa, green beans, hops and potatoes) and now nymphs (immature leafhoppers) can be expected in many parts of southern and central Wisconsin. Even very young nymphs can cause the toxic hopperburn condition after injection of their saliva during feeding. Leaf curling can be the first symptom of hopperburn followed by yellowing and then dead tissue (necrosis) along the leaf margins.
Healthy, vigorously growing plants withstand damage more effectively than stressed plants. Irrigation and cultural practices that favor the crop are recommended. Leafhopper infestations are more likely to occur in crops planted adjacent to alfalfa fields, especially after alfalfa has been harvested and the insects are forced out of the field.
There are several predators, fungal pathogens and parasites that attack PLH, though none have been shown to be effective in controlling the insect. There is very little information available on varietal tolerances to leafhopper damage in hops. In potato we know that round-white ‘chipping’ and also red skin varieties have considerably more susceptibility to damage by PLH moreso than Russet types or yellow-flesh varieties. . In snap bean it has been demonstrated that Blue Lake cultivars are more susceptible to PLH damage than Tendercrop lines. Leaf hairiness has also been shown to deter leafhoppers in alfalfa.
Onion thrips (https://vegento.russell.wisc.edu/pests/onion-thrips/). Thrips are small 1/25-inch insects that cause whitish scratches ‘silvering’ or brownish blotches on plant leaves. Hot dry weather is correlated with severe thrips problems. Thrips attack cabbage and cause a brownish scarring in the head of processing cabbage. Thrips also attack the foliage of onion and must be controlled before significant damage results on leaves or cabbage heads in order to assure unaffected yields.
In onions the injury looks similar to both ozone injury and some diseases. Use larger volumes sprays (20+ gallons/acre) with a wetting agent for adequate coverage and good resulting thrips control. A second treatment 5 to 7 days later is often warranted when adults are present and laying eggs. Most of our foliar applied insecticides do not possess any ovicidal (egg-killing) effects, so a repeat application of the same mode-of-action insecticide is often warranted.
Yellow or white sticky traps (cards) may be used along field edges to monitor the initial migration of thrips into a field. Monitor plants weekly, and scout plants on field edges as thrips are more common at borders in the early part of the season. Depending upon the insecticide being used, it is appropriate to use the correct treatment threshold. When using spirotetramat (Movento HL), abamectin (Agri-Mek SC plus generics), cyclaniliprole (Harvanta 50SL), flupyradifurone (Sivanto Prime) or methomyl (Lannate SP or LV), use 1 immature (larval) thrips per onion leaf as the accepted threshold for chemical treatment. When using either spinetoram (Radiant SC) or cyantraniliprole (Exirel SC), use 1 immature (larval) thrips per onion leaf as the accepted threshold for chemical treatment.
Flea beetles (several species) – (https://vegento.russell.wisc.edu/pests/flea-beetles/). Flea beetles continue to plague several producers, but first generation of many species should be coming to a close. These insects can especially be an issues as an early-season pest, but if good control is not achieved early they can continue their damage for longer than desired.
Several different species are commonly found on all members of the cole crop group, as well as spinach, beets, potatoes, and eggplant. There are several different species of flea beetle that pose problems early in the season when they are considered occasional pests. Host plants of many of the flea beetles are easily identified by their common names. For example, the crucifer flea beetle attacks cole crops and mustards while the eggplant flea beetle is commonly associated with eggplant.
Adult flea beetles overwintered in the soil or beneath plant debris, so early season sanitation is/was critical. Adults have been laying eggs in the soil at the base of host plants in May and into early June. Eggs hatch in 7-14 days and larvae feed on various plant parts until fully grown. They pupate in earthen cells for 11-13 days before emerging as adults. In the adjacent screen shot from the Vegetable Disease and Insect Forecasting Network (VDIFN: https://agweather.cals. wisc.edu/vdifn), it is apparent that the emergence of the next generation of Crucifer flea beetles is soon to arrive in southern Wisconsin. Adult flea beetles are most damaging with two generations typical in Wisconsin. First generation adults develop around 820 FDD and feed through around 1155 FDD. Second generation adults emerge around 1640 FDD and feed through around 1975 FDD.
Colorado potato beetle (CPB) – (https://vegento.russell.wisc.edu/pests/colorado-potato-beetle/). Continue to scout populations of Colorado potato beetle (CPB) as the peak of larval feeding activity is midway across the state at this time. Producers in far northern Wisconsin are just beginning to consider foliar applications whereas producers in the southern quarter of the state are nearing the end of the first generation of larval feeding.
In each instance, the choice of insect control product can vary widely. Northern production areas are finishing perimeter treatments (e.g., indoxacarb) and insect growth regulators (e.g., novaluron), whereas southern locations in southern Wisconsin are now considering second generation options which will begin next week. Recall, there can be considerable variability in the predominant lifestages present, and this often results from planting date (later dates have younger larvae) and proximity to previous year potato (larger larvae in fields close to previous year potato). Continue to refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a list of registered insecticides and management recommendations and recommended products for control are listed in the attached below.
Management options: Insecticide options for managing Colorado potato beetle in Wisconsin.