Hello, and thank you for contacting Ask Extension about your raspberries. Please provide a bit more information so that we can try to diagnose the problem. 

• When did you first notice the symptoms?
• How many/all of your plants involved?
  
• Is there a pattern to the discolored leaves? Top or bottom of the plants? Older leaves or the newest growth?
• Do you irrigate your berries? If so, how often and how much?
• Have you applied fertilizer this year? When, what type?

You can respond directly to this email. I look forward to hearing from you.

On 06/16/2021 8:34 PM Ask Extension <<personal data hidden>> wrote:

 

 

Dear Pete,

Thank you for the additional information. Your raspberries do not seem to be showing any significant signs of pests or diseases. That essentially leaves us with abiotic causes for discoloration such as cultivation practices and environmental causes.

High heat and genetic variability can impact the coloration in the leaves. Other than proper irrigation, sometimes there is little within your control. However, it is important to note that some years are better than others for production. In some areas, there was virtually no strawberry crop this year due to the weather and the same occurred with raspberries a few years ago.

Deficient water in the absence of rain can be an issue. The length of time you irrigate is not as important as the depth of the moisture and the ability of your soil to retain moisture at the level of the roots. Your plants do not seem to show signs of moisture deficiency, but it would be a good practice to test your soil with your finger or screwdriver every few days. Press your finger into the soil 2 inches (do not include any mulch). If soil sticks to your finger it does not need water. Wait a day to check again. If it comes out clean, it's time to irrigate. Here are some additional guidelines:

https://extension.umn.edu/water-wisely-start-your-own-backyard/watering-vegetable-garden#many-ways-to-irrigate-869313

Raspberries require high soil fertility and fertilizing once a year may not be sufficient. There is little scientific evidence to show that foliar application is beneficial to plants. Check your fertilizer label for the recommended application rate, method, and frequency. Use it as directed which usually involves an application to the roots. This will circulate nutrients throughout the plant. Of course, compost and mulch will improve your soil over the longer term by increasing the amount of organic matter. This can reduce the amount of fertilizer required over time.

A last point is that raspberries do not thrive under crowded conditions. Yours may be too dense. It is best to thin the canes to 8 inches apart in spring as early growth starts. This allows for more sunlight and airflow and provides more root space and thus more nutrients per plant. 

Overall, your plants appear healthy. If you notice additional symptoms or a deteriorating condition, please write again.