Soil color

Question: We planted some bell peppers in a raised bed and it seems like they turned the soil all around them a chalky color. Could you please tell us if that soil is now not useable and what the issue could be? The first picture is of the aforementioned soil and the second of the soil elsewhere in the bed.

responder: Linda J. Brewer, Senior Faculty Research Assistant II  Replied September 23, 2024, 3:12 PM EDT
response: It's hard to be 100% positive, but I strongly believe that what we're seeing in photo #1 is fungal mycelia.   The vast majority of soil fungi are beneficial rather than disease organisms. In fact, many antibiotics are derived from fungi - think penicillin.   From my perspective the important question is how did the pepper plant perform? If it did well, you have nothing to fear.  It's entirely possible (in fact probable) that a very localized change in the nature of a soil is the result of the potting mix in which a seedling was grown. Soil microbes (bacteria, fungi) had all summer to feed on the potting mix. It's very common for commercial potting mixes to have a great deal of nutrients added so that the seedling has a robust and vigorous appearance.

responder: The Question Asker Replied September 23, 2024, 3:28 PM EDT
response: Hello, Wow quick response, thanks! The pepper plant planted there did not do well. I pulled out one that was spotted like the attached picture, and the remaining ones produced one-two rotted peppers and did not grow very large.On Mon, Sep 23, 2024 at 12:12 PM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied September 24, 2024, 2:10 PM EDT
response: Hello:  I concur with the first comment that the "chalkiness" of the soil is due to general soilborne fungi that are primarily non-pathogenic.  Based on the limited photos that you provided, it is difficult to determine what factor(s) are resulting in un-thriftiness of the pepper plants and poor pepper fruit yields.  However, your comment that the pepper plants located there did not do well suggests that this is what we call an abiotic problem, meaning that an environmental factor, likely associated with the growing medium, is at fault rather than a plant pathogen causing a disease.    Sometimes when the soil surface shows extension fungal colonization, it can be associated with a combination of very high levels of soil organic matter and too high of fertility applications.  Did you amend the raised bed with compost or some other organic amendments, and if so, was the amendment rate based on a soil fertility test to guide the amount of amendment to add?  Did you apply fertilizer to the plants, and if so, what type and what regime?    The one seedling that is shown with the roots exposed exhibits poor root development as well as some type of wounding on the lower stem.  Sometimes in planting medium that is too high in organic matter and fertilizer, the plants have a water deficiency, especially under high temperature stress.  The plants will grow slowly and the lower stem and the fruit are exposed to the sunlight.  During high heat spells, the exposed soil is quite hot, and between the high soil temperature, high air temperature, and sunlight, the lower stems can be wounded by the heat and sunlight, resulting in wounds.  Also, the fruit that develop on small, slow-growing, unthrifty plants are exposed to direct sunlight, which can lead to sunburn and fruit damage.  The affected spots on the fruit are then predisposed to secondary invasion by fungi and/or bacteria, leading to rotten spots on the affected pepper fruit.  You can read more about sunburn (also called sunscald) at the following links https://pnwhandbooks.org/plantdisease/host-disease/pepper-capsicum-spp-sunburn and https://www.canr.msu.edu/news/hot_and_sunny_days_promote_sunscald_in_peppers_and_other_vegetables  The brown leaves that you observed could also be due to sunburn.  Even if the the growing medium is perfect in condition, bell peppers and other types of peppers are prone to sunburn, especially under period of high temperature.  Raised beds can be even more prone to the effects of high temperatures and soil water deficits, which cans stress vegetable plants and reduce their growth rates.    If the problem was due to a soilborne pathogen, the plants would wilt and eventually die.  Typically there is always a bit of root rot on roots of every plant that I have closely examined.   It is possible that there are soilborne insects that are feeding on the roots, but there are no obvious chewing injuries that I can discern in the one photo.  However, the images offer limited visuals for diagnosis and if you still have affected pepper plants, you should consider contacting the local Master Gardener group in the County Extension Office in your County to see if they can examine a plant sample as well as look at a portion of the chalky soil and provide you with better guidance as to what has affected the pepper plants.  The Multnomah Master Gardener Helpline is <personal data hidden> and they are located at 3880 SE 8th Avenue, #170 in Portland, OR.