Spicy, delicious peppers are much loved by consumers, but a problem called Stip disorder, which damages some pods, is causing heartburn for some producers and processors.
It was first reported and studied in Florida and California-grown peppers around 1995, but there are reports of Stip disorder as early as 1975 in Texas, and it was more recently officially declared in New Mexico and Arizona chile pepper fields.
Researchers and producers as far away as Australia and Israel have published studies describing the problem.
“Stip disorder, is likely caused by a physiological disorder, possibly combined with abiotic stress factors, including hot temperatures,” says Mark Uchanski, vegetable physiologist at New Mexico State University (NMSU) at Las Cruces, who made a formal announcement of the problem in the state at the New Mexico Chile Conference, attended by pepper growers, processors, and industry representatives.
When he asked for a show of hands of those who had seen Stip-like symptoms on farms or at processing facilities, only a few hands were raised. He then displayed a series of ugly Stip-infected chile photos, and asked for another show of hands. More hands were elevated.
Chile peppers are New Mexico’s signature crop, and in the state Stip is more often found in green chiles, infrequently in red chiles, and so far hasn’t been detected in paprika peppers.
“We don’t have exact numbers on financial losses due to Stip disorder,” Uchanski said. “I’ve heard of pepper loads rejected at the processor due to this problem.”
Initial visual signs of Stip include a hazy, orange-red area inside the pepper pod. Later symptoms include depressed, oval dark-brown or black spots (lesions) one-quarter to one-half inch in diameter. The lesions move toward the pod exterior. A cut-open pod with Stip reveals a layer of dead cells.
“The interior of the infected pod interior appears smashed, similar to an accordion,” Uchanski said. “It’s similar to when an apple is cut open and the fruit browns quickly — so does the chile pepper.”
Symptoms worsen during the ripening and post-harvest periods. The brown tissue rarely moves to the pod cuticle (waxy outer layer). Secondary decay organisms are absent in fresh pods. There are no foliar symptoms with the disorder.
Uchanski says microscopic analyses of infected pods have clusters of collapsed (dead) cells. The browning is caused by the release of tissue cell contents combined with oxidation.
There is no sign of a puncture wound from insects or infection. The finger is sometimes pointed at stink bugs, which Uchanski calls a highly unlikely culprit.
Florida and California have gained a great deal of knowledge about Stip disorder since it was first found about 17 years ago, he said.
Stip has been considered a minor problem in New Mexico and Arizona, but Uchanski’s announcement at the conference suggests otherwise — that it is likely a larger and more widespread problem than originally thought.
Several theories offered
Stip is a German word for ‘specks.’ A paper published in Germany in 1892 linked a calcium deficiency in apples to Stip. Others believe Stip is the result of plant transpiration problems tied to water loss inside the plant, which can result in calcium problems.
“We deal with a lot of those situations in the Southwest,” Uchanski said. “Stip is likely tied to a calcium imbalance or deficiency. Stip may be a different expression of a calcium imbalance,” Uchanski explained.
Tim Hartz, University of California-Davis Extension specialist, says Stip disorder has been found in bell peppers in California. Hartz and Uchanski agree the most progressive way to find a solution to Stip is through cultivar selection.
Hartz said the California Pepper Commission funded research on Stip in bell peppers in the late 1990s with several important findings, which he summarized:
- Bell pepper cultivars vary greatly in susceptibility to Stip.
- Stip is generally considered a calcium disorder. This problem is usually most severe under conditions that limit crop transpiration and more so with fruit maturing in fall conditions rather than summer conditions.
- High nitrogen fertilization tends to increase Stip, but environmental conditions appear to be more important than nitrogen status.
- Soil- applied calcium tends to be ineffective.
- Repeated foliar calcium applications may help reduce symptoms but the approach may not be logistically or economically feasible.
“The bottom line is that Stip is a sporadic but potentially devastating problem,” Hartz said. “Avoidance with resistant varieties is the best course. Active management practices to control or prevent the disorder tend to be minimally effective.”
Conditions which can favor calcium deficiency in the Southwest, Uchanski says, include high or low soil moisture; inconsistent water supplies; intense sunlight; hot temperatures; a nutritional imbalance (too much nitrogen and not enough calcium); lush, excessive vegetative growth; and high salt concentration.
“Once in the bin, affected peppers can take a turn for the worse within 24 hours,” he said.
Stip disorder is sometimes confused with blossom end rot (BER) disease found in chile, but Uchanski says BER is not the cause in this case.
BER is a non-infectious disorder caused by calcium deficiency in the pepper pod. Under hot summer conditions, calcium travels with water through the plant, roots, stems, and leaves. The calcium fails to accumulate in the waxy pods.
Several theories exist for Stip causes, Uchanski says, including toxic levels of calcium which can puncture cells leading to brown spots, an unidentified pathogen, and an increase in pesticide applications; particularly nicotine-based products.
The prevailing theory, Uchanski says, is an interaction between extreme summer temperatures and some cultivars.
To gain further knowledge about Stip, Uchanski last year called in the “SWAT Team” – NMSU’s Soil, Water, and Agricultural Testing Laboratory. He provided the lab with plants with and without Stip disorder symptoms. The findings indicated symptomatic pods had higher calcium content than asymptomatic pods.
What happens next? Reliable testing protocols could be developed along with in-field cultivar screening under southwestern growing conditions.
“We could evaluate existing cultivars for resistance or susceptibility and go from there,” Uchanski said. “It’s a discussion we need to have from a plant breeding perspective and determine the severity of the problem in this region.”