Tipburn in Hydroponic Lettuce

By: Dan Gillespie, Technical Specialist

Tipburn is among the most common issues experienced in controlled environment lettuce production. Tipburn occurs as browning of the edges or tips of new young leaves (Figure 1).

Figure 1. Tipburn on young lettuce leaves

Tipburn in lettuce is most often caused by calcium deficiency. However, this deficiencyis usually not a result of insufficient calcium in the nutrient solution. To understand why tip burn occurs (and how to avoid it), we need to understand how calcium travels through the plant

Calcium moves through the plant differently than nearly all other nutrients: It requires mass flow of water. Think of it as a hose that must be turned on for the calcium to move into the plant. Mass flow is driven by transpiration, so high transpiration rates will enhance calcium uptake and translocation, whereas, low transpiration rates will decrease calcium uptake and translocation. When a head of lettuce grows, the growing point becomes enclosed by older mature leaves, creating a high humidity microclimate. This microclimate results in decreased transpiration, which leads to the tip burn.  

The first step in preventing tipburn is ensuring that calcium is not lacking in the nutrient solution and that your fertilizer formula has a proper ratio of potassium, calcium, and magnesium. Source water with calcium concentration above 40 ppm is typically a good candidate for one-part fertilizer systems such as Jack’s Nutrients 12-4-16 RO or Jack’s Nutrients 15-5-20 Tap. However, source water with lower concentrations of calcium will typically require the use of a two-part fertilizer system, such as Jack’s Nutrients Part A 12-4-26 and Cal Nit Part B 15-0-0. Additionally, nutrient solution electrical conductivity should generally not exceed 2.5 mS/cm, as high soluble salt levels will decrease water and calcium uptake. Note that all Jack’s Nutrients provide the proper balance of nutrients.

As stated above, even when calcium levels in the nutrient solution are adequate, tipburn may still occur.  Improve airflow around the growing tip with the use of vertical airflow fans.Vertical airflow should provide just enough air movement to gently move plant leaves (0.3-0.5 m/sec). This will eliminate the microclimate and facilitate calcium uptake.

If vertical airflow fans cannot be installed, another option to prevent tipburn is increasing night time humidity above 95%. High nighttime humidity leads to increased root pressure, and thus, increases water and calcium translocation to the growing point of the plant. However, this strategy can increase the threat of fungal diseases that thrive in high humidity environments. 

Product Name		Item Number
Jack's Nutirents 12-4-16 RO		33-12416
Jack's Nutirents 15-5-20 Tap		33-15520
Jack's Nutirents 5-12-26 FeED Part A		33-51226
Jack's Nutirents 15-0-0 Boost Cal Nit Part B		33-79080

Using Sticky Cards for Insect Monitoring

By: GGSPro Technical Specialists

Sticky cards are the best monitoring tool available for flying insects, such as thrips, fungus gnat
adults, shorefly adults, whiteflies and winged aphids. Using cards for active monitoring of these pests supports proactive decision making for best management of pest populations.

Sticky cards are available in solid yellow, solid blue, and bi-colored forms (two-sided, yellow on one side and blue on the other). Some sticky cards are pre-printed with a grid pattern that allows for quicker counting. Sticky cards come with a protective sheet that is removed to expose the sticky surface. To make these easier to work with, take a tip from the pros and keep your sticky cards refrigerated until use.

Proper use of the cards will generate the best data. Prior to placing cards in the crop, date and number each card with a consistent location code. Sticky cards should be placed above the crop with one third of the card in the canopy. Additionally, place some cards vertically just above the crop canopy; avoid placing sticky cards too high above foliage to ensure you pick up all flying insects. To monitor for insects emerging from the media (e.g. thrips and fungus gnats), place yellow sticky cards horizontally just above the media surface. Growers generally use 1-2 cards per 1000 square feet, increasing to 3-4 cards per 1000 square feet when monitoring for thrips or when monitoring higher value crops. Remember to place additional sticky cards near doors, vents or areas of concern.

Perform weekly counts of pests and beneficials captured on the cards, using a 16x hand lens to identify the insects. When recorded, this data can be analyzed for population trends on which management decisions can be made. Be sure to note any specific weather patterns in your records, too. Cards are generally replaced weekly. However, when pest activity is low, cards may be used for several weeks. If used over multiple weeks, take another tip from the pros: Use different colored Sharpies to circle and count the pests each week so you are sure to only count the new pests in later weeks.

Speaking of beneficials, when releasing Aphidius, Encarsia, Eretmocerus or Orius, take cards down on the day of release to minimize capture of the good bugs. Return the cards to the crop a few days after release.

Product		Item Number
2-color blue/yellow sticky cards, 4"x5"; 10 per pack		74-3668
Yellow moisture resistant monitoring cards, 3"x5"; 50 per pack		74-36705
Trapline T Yellow Roller trap 6"x328'		SB8051-05
Sticky yellow trap roll 12"x300'		74-12300
Sticky yellow trap roll 6"x1500'		74-61500
Sticky blue trap roll 6"x1500'		74-61500B