MSU Extension Vegetables

You are in the final stretch of the pumpkin season in Michigan. Vines are dying down and cutting has begun. It is at this point you discover just how well your growing season management practices paid off. It is easy to get nervous right before the October rush. We are often asked when pumpkins should be harvested and what can be done for certain issues now, but the problems that are discovered now are often symptoms of poor early season management or environmental conditions

Powdery mildew and Plectosporium blight

Poor control will result in defoliation, sunburned fruit and weak, brown handles. There is limited effectiveness with rescue sprays.

Worth spraying now? YES, if leaves, vines and fruit you intend to harvest are still green. Poor handle quality can make fruit unmarketable.

What to use? Spray programs should start in August when heavy dews began to form, and continue through seven to 10 days before harvest, rotating between at least two of those products with different FRAC codes and tank mixed with Bravo Weatherstik [2 pints per acre, zero-day pre-harvest interval (PHI), FRAC M5] and a surfactant. The most effective products available include:

• Inspire Super (16-20 ounces per acre, 7-day PHI, FRAC 9 and 3)
• Pristine 39WG (12.5-18.5 ounces per acre, 0-day PHI, FRAC 7 and 11)
• Procure 50WS (4-8 ounces per acre, 0-day PHI, FRAC 3)
• Quintec (4-6 ounces per acre, 3-day PHI, FRAC 13)
• Rally 40W (2.5-5.0 ounces per acre, 1-day PHI, FRAC 3)
• Vivando (15.4 ounces per acre, 0-day PHI, FRAC 50

Fruit rots

Fruit rots are triggered in some fields by August rains. This is usually caused by a Phytophthora population in the field. Whenever it makes sense for your customer-base, avoid the round-stemmed Cucurbita maxima species in fields that are known to have a history of Phytophthora, as they are very susceptible to fruit rots. The ridge-stemmed Cucurbita pepo and Cucurbita moschata species have some level of age-related resistance that can allow older fruit to hold off the rots longer than younger fruit. This is noticeable in later planted small-fruited hard squashes since they are still young during the August rains, and resistance has built some earlier planted and larger-sized pumpkins that are further along in their fruit growth.

Worth spraying now? NO. Michigan State University Extension and AgBioResearch trials found that a preventative application at fruit set, and a second application 14 days later was an effective measure for managing this disease. If wet conditions persist, another application may be necessary. A minimum of 40 gallons per acre with a boom sprayer, or an air blast sprayer is best to penetrate the canopy and make contact with the fruit itself. A soil drench is ineffective for fruit rots. Rotation away from other fruiting vegetables, including beans and peas, is extremely important for preventing this disease from spreading each year.

What to use? The following products are effective against Phytophthora when applied proactively, and rotated:

• Forum 4.18SC (6 ounces per acre, 0-day PHI, FRAC 40)
• Gavel 75DF (1.5-2.0 ounces per acre, 5-day PHI, FRAC M3 and 22)
• Orondis Ultra (4-8 ounces per acre, 0-day PHI, FRAC 49, and 40)
• Presidio 4SC (3-4 ounces per acre, 2-day PHI, FRAC 7 and 11)
• Revus 2.09SC (8 ounces per acre, 0-day PHI, FRAC 40)
• Zampro (14 ounces per acre, 0-day PHI, FRAC 45 and 40)

Fruit spots

Spots that show up on fruit are usually due to Angular leaf spot and bacterial leaf spot. Both caused by seed borne bacteria that infect leaves first and fruit later. However, once established in a field, avoid planting pumpkins there for two to three years. Mild cases are not much of a concern but in severe situations the spots can coalesce and lead to fruit rot. For more information, refer to “Bacterial disease of pumpkins: An old enemy and an emerging bacterial disease” by MSU Extension.

Worth spraying now? NO. Control at this time is of no value. Preventative application of copper formulations can reduce severity of disease development, and is more effective than sprays after symptoms have developed. MSU Extension recommends spraying fruit when softball sized until fruit set is complete.

What to use? Different copper formulations are available, but for all products, the tank mix solution should be in a pH range of 6.5 to 8 to decrease the risk of phytotoxicity in vine crops. Bacteria can develop resistance to the copper mode of action (FRAC M1). Alternate and tank mix with other products, such as:

• Mancozeb (various formulations, 5-day PHI, FRAC M3)
• Actigard 50WG (0.5-1.0 ounces per acre, 0-day PHI, FRAC 21)
• Tanos (8-10 ounces per acre, 3-day PHI, 32 ounces per acre per season max, FRAC 27, 11)
• Serenade Max WP (1-3 pounds per acre, 0-day PHI, FRAC 44)

Cucumber beetles and squash bugs

These insects are very damaging to seedlings and control is most important just after planting. Mid-season growth is more tolerant of feeding damage, but plants can be impacted by bacterial wilt disease transferred by the beetles, and cucurbit yellow vine disease from squash bugs. If plants have made it this far, the last remaining impact they can have is fruit rind and stem feeding.

Worth spraying now? MAYBE. A lot depends on when you are going to harvest. If the fruit is orange and ready, save yourself some money and just harvest. Control would only be necessary if you have a significant number of fruit in the green to orange transition phase and live in the southern tier of counties, and damage can be readily found.

What to use? Pyrethroids are the primary mode of action (IRAC 3A) for handling these pests mid-season:

• Ambush 2EC (3.2-12.8 ounces per acre, 0-day PHI, 6.4 pounds max per season, RUP, IRAC 3A)
• Assail 30SG (2.5-5.3 ounces per acre, 0-day PHI, 5 applications max per season, IRAC 4A)
• Brigade 2EC (2.6-6.4 ounces per acre, 3-day PHI, 19.2 ounces per season max, RUP, IRAC 3A)
• Mustang Maxx (2.8-4 ounces per acre, 1-day PHI, 24 ounces per season max, IRAC 3A)
• Pounce 25WP (6.4-12.8 ounces per acre, 0-day PHI, max 4.8 pounds per season, RUP, IRAC 3A)
• Warrior II (1.28-1.92 ounces per acre, 1-day PHI, 11.5 ounces per season max, RUP, IRAC 3A)

Aphids

Aphids are a major vector for viruses, which twist foliage and makes odd-shaped fruit if they transfer the virus before pollination and fruit set. If aphids colonize after fruit set, the primary issue is defoliation and the sugary honeydew they drop onto developing fruit. This sugar gets colonized by a black sooty mold. The mold does not infest the pumpkin, but makes post-harvest cleaning more important.  

Worth spraying now? PROBABLY NOT. Unless your vines and fruits are still green, it will not be economical to spray them now so close to harvest. If they are in the field in low numbers right now, lady beetles hover flies and parasitic wasps will handle them from here to the end of October. If colonies have grown to form hotspots in your field, then couple of weeks ago would have been more appropriate timing.

What to use? Scouting and spot treatments can save money by preventing their spread and future field-wide applications. The following products are applied to the foliage:

• Actara 25WDG (1.5-3 ounces per acre, 0-day PHI, IRAC 4A)
• Assail 30SG (2.5-4 ounces per acre, 0-day PHI, 5 applications max per season, IRAC 4A)
• Beleaf 50SG (2-2.8 ounces per acre, 0-day PHI, IRAC 9C)
• Exirel 0.83E (13.5-20.5 ounces per acre, 1-day PHI, IRAC 28)
• Fulfill 50WDG (2.75 ounces per acre, 0-day PHI, 5.5 ounces max per season, IRAC 9B)
• Malathion 5EC (1.5-2.8 pints per acre, 1-day PHI, IRAC 1B)
• Warrior II (1.28-1.92 ounces per acre, 1-day PHI, 11.5 ounces max per season, RUP, IRAC 3A)

The following products can be used through drip irrigation lines if a field-scale outbreak occurs early in the season, but should be avoided once flowering begins:

• Admire PRO 4.6DF (7.0-10.5 ounces per acre, 21-day PHI, 10.5 ounces max per season, IRAC 4A)
• Platinum (5-11 ounces per acre, 30-day PHI, IRAC 4A)
• Sivanto 200SL (21-28 ounces per acre, 21-day PHI, IRAC 4D)
• Verimark 1.67SC (10.0-13.5 ounces per acre, 1-day PHI, IRAC 28)

Sunburn

When plants lose their leaves because of natural senescence or from disease, or fruits are cut from the vine to field cure, the top sides of fruit can be damaged by the sun on cloudless days with low humidity. Uncured fruit are damaged the most, with shorter exposure to bright sun. Fruit can look fine in the field then show symptoms once harvested. The first sign is slight skin discoloration, followed by a sunken area that occurs within a few days.

What to do? Harvest pumpkins to cure in dappled shade or full shade, or keep vines health from diseases to cure in the shade of their own leaves. This is similar to hardening off transplants in the spring, but for fruit at the end of the season.

Frost damage

Pumpkins are susceptible to frost damage too. The Lower Peninsula averages first frost around Oct. 15. Some years we get our first frost by mid- to late September. The northern Lower Peninsula and Upper Peninsula will often receive their first frost earlier. The damage looks like water-soaked spots on upper surface of fruit which soften the rind. Badly damaged fruit will eventually collapse in on itself. Ornamental and winter squashes may still harden, but others will soften and rot.

What to do? Maintaining green leaves in the field will help shield fruit from frost, and covering a wagon load or pile in the yard will protect harvested fruit.

Will my fruit make it?

Pumpkins have a range of maturity times, determined by genetics and environmental conditions. You should aim for 50% mature fruit by Sept. 15, and all mature fruit by Oct. 1. Most varieties grown in the Midwest are marketed with an average maturation time between 85 and 105 days. This means that in order to target the market for the seven or eight weekends in September and October in Michigan, you need to plant the longest-maturing varieties in the last week of May and the fastest maturing varieties in the first or second week of June at the earliest. Transplanting pumpkins in those windows will advance your harvest up by about another two weeks.

The last reasonable time to plant pumpkins in Michigan for a good harvest is around July 4 for seeds and July 11 for transplants. Most pumpkins would still ripen before mid-October and allow for sales more evenly distributed across weekends. But, this is not an ideal planting time because these later plantings will result in a glut of pumpkins too late, and with too few sales opportunities.

After planting, environmental conditions can then begin influencing plant growth. According to "The Physiology of Vegetable Crops" by H.C. Wein, “Conditions which foster stem extension and reduce carbohydrate build-up, such as high temperatures, low light conditions, high nitrogen levels and close plantings, also increase the tendency for male flower production in cucurbit vegetables.” Male flowers will not set a fruit, and if those conditions persist, then fruit set is delayed until female flowers are produced and pollinated. Temperatures below 50 F and over 85 F will negatively impact pollination because temperatures beyond those limits are not favorable to bees. After flowers are pollinated, fruit can take 45-60 days to mature.

In 2019, many growers were delayed in planting pumpkins. Some had to plant in mid-July. Will their pumpkins make it? Pumpkin fruits can grow much faster if the plant has fewer fruit and reach maximum growth rates around 75 F. The closer daytime and nighttime temperatures swing to that optimal temperature, the faster fruit will grow. Hot days and little rain after July resulted in poor fruit set on some farms. Depending on the fruit set, the ultimate size of the pumpkin variety, and temperatures over the next few weeks, some will make it and some will not.

Picking and marketing

This is going to be your main focus from now until Oct. 31. The best quality pumpkins are cured in the field in dappled shade of their own leaves. It is of utmost importance to maintain green plants as long as possible, to allow fruit to mature on the vine. If the leaves are dying and the fruit is over 50% orange, it is best to harvest. Pumpkins harvested earlier than 50% orange eventually turn dull orange, but they do not become hard, mature fruit and they rot easily. 

Getting them out of the field and into a dry, somewhat shady area will allow for curing without as much risk for sunburn, insect infestation and possibly some fruit rots. Cut them from the vines and clean off as much soil as you can. If you suspect fruit rots may become an issue it would be best to place them in a 10% chlorine dip if you can. This will not guarantee the fruit will not rot since some fruit rots can be systemic. Avoiding harvest in wet areas completely or keep that fruit separate from fruit harvested from other areas of the field. This will minimize fruit to fruit contamination.

Remember, “Volume sells.” People are attracted to large displays, so keep them well stocked and remove rotting pumpkins as soon as you see them. Especially make sure to have displays in great shape for the weekend. This is even more critical if the weather is expected to be nice. There is a direct correlation between nice weekend weather in October and pumpkin sales. You will have left overs come Nov. 1 when the price drops. Just consider that as one of the costs of doing business.

The overriding message in this article is to not get the urge to go into coasting mode for the next four weeks. You have brought your pumpkins through a lot over the past four months, to give up now might mean the difference between a good year and a great year.