June 13, 1976: an F5 tornado near Luther, Iowa, was one of the largest in state history. The tornado, nearly a mile wide, spawned multiple satellite tornadoes and caused widespread destruction between Boone and Ames, demolishing over 60 homes and 300 farm buildings. Charles Barthold’s iconic photographs of the event contributed to tornado science and earned him a Peabody Award.

• Expect continued warmth with a risk of extreme heat in the coming week.

• An active precipitation pattern is forecast, with widespread rain likely. Most of Iowa should receive at least an inch of rain between June 12–19; northern areas may get up to 2 inches, especially with thunderstorms.

• The Climate Prediction Center’s outlooks (6–10 day, 8–14 day, and 3–4 week) all lean toward above-normal temperatures and slightly above-normal precipitation.

• There is a slight risk for extreme heat (June 19–21) and heavy precipitation (June 19–22, especially in northern Iowa).

• The past two weeks were cooler than normal, averaging 65°F (2–4° below normal).

• On June 11, hailstorms hit northern Iowa (Palo Alto, Kossuth, Hancock Counties), causing severe crop damage and total losses in some corn and soybean fields.

• Aster Yellows in Garlic and Other Crops:
  Aster leafhopper infectivity for aster yellows has jumped from near zero to 15–20% in Michigan, exceeding last year’s rates. Growers should watch for symptoms in garlic, flowers, and lettuce. One Iowa garlic grower observed premature yellowing and is testing for the disease; comparison with seed garlic from another location suggests possible infection.

• Squash Yellowing (B Gene):
  Yellow leaves in squash during cool weather may be due to the B gene, which breeders retain for its positive effects (fruit color, yield, virus resistance). The B gene can be identified by a yellow stem on yellow squash.

• Onion Thrips:
  High thrips numbers reported in onions and mulberries. Thrips are tough to control; Dan recommends using azadirachtin (from neem), horticultural oil, a spreader-sticker, soil-drench nematodes, and mycopesticides (Beauveria bassiana). Control is important because thrips damage increases storage rots.

• Aphids:
  Aphids can multiply rapidly, especially under row covers. Dan suggests treating transplants with insecticidal soap (e.g., M-Pede) before planting and repeating the spray after five days. In the field, use water sprays, insecticidal soap, oils, and azadirachtin. Tank-mix treatments after jar testing. Attract beneficial insects with sweet alyssum and other flowers, especially in tunnels or greenhouses.

• Squash Vine Borer:
  The pest is now active in central Iowa. Remove row covers from flowering squash, scout for eggs at the stem base, and use BT sprays or manual removal of larvae. Large fields are less affected; small plantings are at greater risk.

• Tomato Yellow Shoulder Disorder:
  This disorder is more common in hot weather and is linked to potassium deficiency and high fruit temperatures. Dan recommends ensuring adequate potassium and using shade cloth in high tunnels to keep fruit shoulders cool. Some cultivars are more susceptible.

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