Choose Disease Resistant Fruit and Nut Varieties When You Can

(News article for July 25, 2019)

In last week’s article about following the “right plant, right place” principle, I talked about choosing fruit plants that are well-suited to our temperatures, including minimum and maximum temperatures, as well as the number of chilling hours that we get. This week, I’ll address choosing fruit nut varieties that are resistant to common diseases.

Our high rainfall conditions mean that southeastern Louisiana is favorable for many plant diseases. With few exceptions, water on leaves typically favors leaf spot diseases, and water around roots generally favors root rots.

Choosing disease resistant varieties is a way to avoid many plant disease problems. In some cases, this prevents the need to spend time and money on applying fungicides or bactericides. In some cases, though, there are no good pesticide options for these diseases, even if you don’t mind applying them.

One of the first examples that comes to mind relates to fire blight of apples and pears. Fire blight is a bacterial disease that is a problem in much of the US. Bacteria infects through flowers, and once people see the characteristic burnt-looking shepherd’s crook symptom, it’s too late to apply a bactericide to prevent blossom infection in the current year. Fire blight is one reason that pear varieties like ‘Baldwin’ and ‘Orient’ are recommended for southern Louisiana, while many of the ones that we see in the grocery store, like ‘Barlett’, are not.

Among blackberries, we’re fortunate that thornless, upright-growing varieties like ‘Arapaho’, ‘Natchez’, and ‘Osage’ tend to be resistant to two of the most problematic blackberry diseases, rosette (double-blossom) and orange rust. ‘Navaho’ is an exception – it’s susceptible to orange rust.

In case you ever wondered why we don’t tend to grow grapes like ‘Chardonnay’ or ‘Merlot’ here, it’s largely because of a bacterial disease called Pierce’s disease. Muscadine and rabbiteye blueberry varieties, in general, tend to be more disease resistant or tolerant than bunch grape and southern highbush blueberry varieties, respectively.

When choosing pecan varieties for home orchards, one of the most important considerations is resistance to pecan scab. While commercial growers can spray fungicides for this if they desire to do so, home growers typically do not have the equipment needed to get good fungicide coverage in the canopy of a large pecan tree. Considering this, the varieties ‘Caddo’ and ‘Oconee’ (Type I), and ‘Candy’, ‘Elliott’, ‘Melrose’, and ‘Sumner’ (Type II), are some of the varieties recommended for home plantings.

I’ll address disease resistance in vegetables next week.

Contact Mary Helen.

pecan scab symptoms on leaf

pecan scab symptoms on shuck

Pecan scab problems can be avoided or minimized by planting scab-resistant varieties. (Photo sources: [top] Jonas Janner Hamann, Universidade Federal de Santa Maria (UFSM), Bugwood.org; [bottom] Rebecca A. Melanson, Mississippi State University, Bugwood.org)

7/25/2019 4:00:40 PM
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