​Roots, Shoots, Fruits & Flowers: Ponderosa Lemon, Dry Sacs in Citrus and Squash Vine Borer

217_fig_1_ponderosa_lemonjpgPonderosa lemons.
Photo: University of California, Riverside.

Ponderosa lemons

Mike emailed with his question, “Do you know any local nursery that has hearty ponderosa lemon plants?” AHA was able to find a local nursery with the “ponderosa” lemon and referred the gardener to the nursery. Then AHA was curious to learn more about this variety of fruit.

According to our friends at Texas A&M, “'Ponderosa' is not a true lemon although its fruit are much like citrons and lemons. It originated as a chance seedling during the 1880's. 'Ponderosa' trees are rather small and somewhat thorny; its fruit are very large and seedy, with yellow, thick, bumpy-textured peel. 'Ponderosa' is more cold-sensitive than true lemons.”

However, The Northwest Master Gardeners had a 2017 garden tour, and one of the stops featured a “ponderosa” lemon in one of the gardens of Shreveport. The “take home” message may be that this variety of lemon is more cold-hardy than originally reported by reputable sources.

217_fig_2_dry_spots_in_navel_orangejpgSliced navel oranges with dry spots encircled.
Photo: Keith Hawkins, LSU AgCenter

Navel oranges with dry spots

Charles brought in a navel orange with “dry spots” to the AgCenter and wanted to know what was happening to his fruit.

An online search resulted in useful information from the University of Arizona Cooperative Extension (UACE). The condition shown above is called “Dry Juice Sacs” or “Granulation”, and the publication from UACE reports, “Oranges, grapefruit and tangerines are affected; especially those budded on rough… rootstocks. Cold injury may also result in granulation of fruit.” University of Florida also reports, “Granulation usually occurs on rapidly growing fruit and excessively large fruit.” The management for this citrus disorder includes, “Good fertilization and nutrition practices and early seasonal harvesting may alleviate this problem.”

217_fig_3_squash_vine_borerjpgSquash vine borer, an adult moth (left) and the larva (right).
Photo: University of Illinois at Urbana.

Control squash vine borer

Christy is looking for organic treatments to control squash vine borer (SVB), “Do you know much about using beneficial nematodes to control squash vine borer pupa in the soil? “

The SVB is a moth, and the female tends to lay its eggs near the base of the squash stem. The larvae hatch and then bore into the stem. As the larvae mature, they become larger and cause more tunneling in the squash vine.

The Home and Garden Information Center of the University of Maryland presents an array of control measures to include organic, cultural, and chemical methods:

  • Plant early to lessen injury. Use transplants instead of seeds. Or, plant squash seed mid-June. [This recommendation probably is irrelevant for Louisiana.]
  • To prevent egg-laying, wrap a collar of aluminum foil around lower stems or dust or spray lower stems with spinosad or pyrethrum.
  • Cover plants with floating row cover until flowering.
  • For active borers, make a vertical slit upward from where frass is observed. Use a razor or sharp knife and cut half-way through the stem. Remove and kill borer. Mound soil over the wound to induce supplemental rooting.
  • Spray lower plants stems and base of plant with pyrethrins when adults are flying (mid-late May). repeat 14 days later.
  • Bt (Bacillus thuringiensis) or beneficial nematode Stinernema carpocapsae can be injected into wound to kill borers.
  • Seal up infested vines in plastic bag before larvae pupate (break life cycle.)
  • Butternut and cushaw are resistant, yellow crookneck less susceptible than zucchini.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or khawkins@agcenter.lsu.edu. Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

2/18/2020 1:59:32 PM
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