2021 Considerations: Probing Pepper Production

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

Our biweekly crop by crop prep series wraps up with some sweet and spicy pepper information.

Temperamental with temperatures

Peppers are notoriously picky plants that need a specific set of temperatures to grow and produce fruit successfully. Here are some problems we typically see related to temperature in peppers, along with solutions.

• Peppers need high temperatures for germination. We’ve already seen some reports of stunted peppers, or very very slow to germinate peppers. If your peppers are lagging, it’s not too late to add some more heat to help them catch up. The ideal temperature for vegetative growth of peppers is between 77 and 80 degrees fahrenheit during the day, and 64-68 degrees fahrenheit at night (Wein, 1997),
• While peppers do need to be hardened off, they are sensitive to over-hardening, which can delay growth in the field and reduce yields. Do not harden off your peppers for more than 7-10 days (Source: University of Georgia Commercial Pepper Production Handbook). While the forecast can change significantly over a 7-10 day period, keep an eye out for heavy rainfall or cold fronts in the forecast as you decide when to begin the hardening process so that you don’t need to hold your peppers for too long once you begin the process.
• At the time of transplanting, we often see peppers turn purple due to a lack of phosphorus uptake. However, it rarely means there is not enough phosphorus in the soil (many MN vegetables have way too much phosphorus in the soil). As long as you’ve done a soil test recently and are managing accordingly, fear not. Phosphorus is less mobile in cooler soils, and as the soil warms up it will become more available. Make sure to wait until soils reach 60-65 degrees F to transplant to avoid problems.
• When peppers begin to flower, high temperatures (~90 degrees fahrenheit) result in blossom and fruit drop. This is significantly exacerbated by drought stress, so make sure to provide plenty of water during bouts of high temperatures. Mulching the soil with a light-reflecting mulch like straw can also help to keep peppers cool.

Pepper blossoms drying up and dropping. Photo: Natalie Hoidal

Flowering issues

Nitrogen

Peppers are moderate nitrogen users (140 lb/acre in low, 120 in medium, and 100 in high organic matter soils), but too much nitrogen at the wrong time can result in poor yields. Peppers are particularly sensitive to flushes of nitrogen availability just before flowering. Too much nitrogen at this period signals the plant to continue producing vegetative biomass rather than shifting into reproductive mode. For this reason, the nutrient management guide suggests applying half of the required nitrogen up front, and half after the fruit have already begun to form. For organic growers using slow release fertilizers, you can apply all of your fertilizer up-front.
 

Pollination

While peppers are technically self-pollinating, they tend to produce more fruit and more seeds when insect pollinators are present. Some growers have started saving pepper seed, particularly for very hot varieties, which tend to be quite expensive. If you’re saving seed and using exclusion cages or bags to prevent cross-pollination, consider adding bees to your exclusion cages.
 

Pepper Meltdown - What’s Actually Happening?

Sunscald on a bell pepper. Photo: Marissa Schuh, University of Minnesota.

As peppers set fruit, there are often concerns about mushy spots and alarming black fuzz on fruit. While the first instinct is often that this is caused by a disease, it is often a physiological disorder at the root of the problem.

Sunscald is an issue in peppers in a way that it isn’t in any other vegetable. It is easy to identify shortly after it happens: look for flattened, tan areas on the sides of fruit exposed to the sun.

However, the longer these fruit are on the plant, the longer the damaged tissue is exposed to moisture and opportunistic bacteria and fungi in the environment. The weakened tissue can get infected by all kinds of secondary pathogens that can cause the original sunscald site to become covered in spores, and the entire fruit to get soft.

Sunscald has provided an entry point for pathogens. Caption: Howard F. Schwartz, Colorado State University, Bugwood.org

Sunscald can be somewhat varietal, so if one variety isn’t super leafy and has lots of mushy peppers, that could be a clue that sunscald is the original culprit.

These fruit will never be marketable, so they can be removed to focus the plant's energy on marketable peppers.

The same series of events can happen with blossom end rot. This symptom of calcium deficiency, whether caused by lack of calcium or lack of water to move calcium, produces underdeveloped areas on the pepper fruit. These rotted spots provided an entrypoint to opportunistic pathogens, which can lead to total pepper meltdown.

Blossom end rot on bell peppers, some of which are already showing signs of secondary infection. Photo: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

Blossom end rot tends to be the worst in the initial set of fruit, so lots of mushy peppers early can be a clue that blossom end rot is the original issue. Pick off these fruit so that the plant stops wasting its energy on them. The issue often self-corrects for the next round of fruit set.

These physiological issues are far and away the most common causes of mushy pepper spots. While diseases like alternaria, anthracnose, and phytophthora can attack pepper fruit, it isn’t common.

Bacterial Spot

Compared to their relatives tomatoes and potatoes, peppers have much fewer disease issues. Bacterial spot is the most common disease we see, and with its ability to infect leaves, blossoms, and fruit, it can be devastating. Like in tomatoes, this pathogen is best managed during transplant production. The close plant spacing, seedborne nature, and warm, wet conditions of the greenhouse can allow for one infected transplant to become a tray of infected transplants. Keep an eye out for transplants with discoloration and water-soaked lesions, and remove these plants and their neighbors.

Photo: Bacterial spot symptoms on pepper plants in the field. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org.

If symptoms appear in the field, remove infected plants, as bacterial diseases cannot be cured. Avoid moving around in fields when plants are wet, as bacterial diseases move with water.