Help my Italian flat been plants with advice on foliar spray

Question: My Italian broad beans are stressed, leaves turning yellow, but still producing. How do I help these plants? Google says it may be a nutrient deficiency of Magnesium or zinc (older leaves seem to be more impacted), and that I should apply the Magnesium or zinc as a foliar fertilizer sprayed on leaves. They are in broad sun all day, from about 10 am until about 7 pm. This theory of low nutrients is possible because the beans are in a newly turned (previously lawn) plot. Perhaps the soil was not as well amended as it needed to be? IF it is nutritional deficiency, which foliar spray fertilizer do you recommend? I see that Miracle Gro has both Magnesium and zinc in it, but I have only used organic fertilizer in the past, such as fish emulsion, which looks like it is mostly nitrogen with only trace amounts of magnesium . Should I be watering more intensively? I thought beans usually like it dry and hot. What do you recommend I do?

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 17, 2024, 4:27 PM EDT
response: It's hard to tell for certain from the images, but a common culprit of leaf paling in beans and other summer vegetables is an outbreak population of spider mites. Mites tend to thrive in hot, dry weather and on plants that are under-irrigated. You can inspect the leaf undersides closely (with a magnifying glass or loupe, if you have one), or tap/flick leaves sharply over a white piece of paper to look for mites crawling around. (Folding or smearing the paper can kill the mites and help make their stains easier to see, though they'll still be tiny.)  If present, the simplest approach is to blast them off the foliage using a strong spray of plain water from a garden hose (make sure any hot water is flushed-out first). It won't get rid of all mites, but it can reduce the population. While low-toxicity insecticide sprays like horticultural oil or insecticidal soap can also kill mites, neither can be applied while temperatures are above 85 degrees, and when plant foliage damage is heavy, such sprays can injure them further, even if they still work to remove mites.  It is possible a nutrient deficiency is overlapping with mite damage, especially if the plants were not fertilized outside of amending soil with compost (which by itself tends to be comparatively low in nutrients, even though it's beneficial to use). Leaf yellowing is sometimes hard to diagnose in terms of which exact nutrient is lacking, since there is some overlap in symptoms, though a laboratory soil test might shed some light on which may be low in the soil itself, and whether the soil acidity level (pH) is where it needs to be for the health of the crop. (For beans, 6.5 is good, though anywhere between 6.0 to 7.0 should be fine.)  Beans don't need much nitrogen applied since they can fix their own nitrogen themselves, though depending on whether the transplants were inoculated with nitrogen-fixing bacteria at the time of planting, applying some nitrogen may give them a boost. To address chlorotic yellowing on older leaves, manganese, magnesium, or zinc may be needed to resolve it. Avoid fertilizing with anything quickly absorbed (like a liquid application to the foliage or soil) until the mites are addressed, since nutrient supplementation (especially nitrogen) can benefit the mites.  Bean plants do not want to dry out; keep the soil moist by feeling it a few inches deep and watering well once it begins to feel somewhat dry to the touch at that depth. When pods develop, it's especially important that the roots are not too drought-stressed, and most of Maryland is significantly behind on rainfall thus far this year.  If mite control and fertilization are working, don't worry if the current foliage does not look any better for it...leaves cannot heal from damage, nor can they always replace nutrients that were lost due to deficiency. If new foliage continues to look good and unaffected, then you can assume the issue is resolving itself.  Miri

responder: The Question Asker Replied July 19, 2024, 10:04 AM EDT
response: Thanks for the info on water, we'll water more deeply , and thanks for the info on mites, we found some and used the jet stream method to blast them. How many times should we blast them with the hose? How long after this blasting off treatment would you say it would be safe to use Neem oil spray as a follow on?   How long after mite amelioration would you say to wait before fertilizing? Can you answer our question about which type of foliar spray would be better, fish emulsion, miracle gro, or something else? And when and how to apply foliar spray?  Thanks for your help, Best, Maryann      On Wed, Jul 17, 2024 at 4:27 PM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 19, 2024, 11:13 AM EDT
response: Since it's plain water, you could spray them daily if you wanted, though that's probably not necessary. You may just have to see when it looks like mites on the leaf backs remain minimal. Since the leaf damage cannot heal, there is the potential at any time for a neem oil treatment to "burn" those leaves with heavy mite damage, but that's unavoidable. At the very least, wait until there is a period of temperatures below 85 degrees to spray, since above that temperature, oil sprays can injure even healthy foliage.  We don't have a specific fertilizer recommendation, but don't spray the foliage, water the roots with the solution, because foliage uptake of nutrients is minimal compared to roots. You can probably apply fertilizer within the week after knocking-down the mite population with water and/or horticultural oil (neem or another). The exact formulation won't matter too much, as long as the fertilizer contains N-P-K as well as micronutrients like manganese, magnesium, iron, and others. Fish emulsion will probably be too weak and incomplete as far as containing enough different types of nutrients. In either case, follow the directions on the fertilizer label for dilution rate.  Miri