Dealing with flood damaged feed crops

// Pasture and Crops

Flood damaged winter feed crops pose challenges for farmers heading into winter, so Beef + Lamb New Zealand asked PGGWrightson Seed’s veterinary nutritionist Charlotte Westwood and extension agronomist nutritionist Wayne Nichol for some management advice.

tractor with winter feed

The pair detailed steps flood-affected farmers could consider when dealing with water damaged crops. These include carrying out a feed budget, prioritizing water damaged crops, re-transitioning stock back onto crops and paying extra attention to on-going crop health, stock health, feed allocations and personal and staff safety. 

This is the summary of Charlotte and Wayne’s advice. More detailed information can be found at PGGWrightson’s The Rumen Room Facebook page

Key management ideas

1) Update Feed Budgets now.
2) Assess winter feed crops.
3) Monitor winter crop well-being for developing damage.
4) Check for flood water contaminants.
5) Plan grazing of crops.
6) Plan for potential animal health issues.

1)  Update feed budgets now. Factor in potential losses of not only winter crop, but also damaged pasture and supplementary feed. It pays to be ruthless. Water-damaged supplementary feed may not be suitable for feeding. Re-assess crops for drymatter yield now and again later in winter as plants may be lost due to disease or the crop may stop growing due to a lack of plant available nitrogen in the soil.

  • Prioritise stock classes. Consider your options using the feed you have on-hand to maintain the condition of stock. If there is a short-fall in feed, take steps to rectify. There are people and funding available to help. Call 0800BEEFLAMB

2) Assess your winter feed crop. Review the extent of the damage on a paddock-by-paddock basis. Look for plant losses (washed away or lodged), areas still underwater or draining and assess areas that may be suitable for grazing.

  • Assess infrastructure damage. Troughs may need cleaning if contaminated by flood waters and may need “footing material” if surrounding soil is very wet.
  • Is kale still standing or has it lodged or washed away? Check if swede, turnip and fodder beet crops are still anchored and whether or not they are covered in silt.
  • Check underfoot conditions. Are their areas that need to be fenced off or grazed later when they dry out?

3) Winter crop well-being. Monitor crops regularly over the coming weeks to assess plant survival, drymatter yield and the feed budget. If multiple paddocks are involved, a ranking system might be useful. Decide what paddocks need to be grazed earlier and which can left until later in winter.

  1. Damage to crops from flood waters depends on how long the crop was underwater. Longer than 48 hours means the crop is at risk of soil oxygen depletion with reduced oxygen available to the roots, increasing the risk of plant loss.
  2. Plant damage is worse when flood waters have ponded. Based on experiences in previous floods, pastures may last up to six days underwater but in Southland, winter feed crops underwater for three days or more were found to be more likely to fail. This could have been exacerbated by ponded water heating quickly due to the summer sun.
  3. While hard to predict, swede crops may survive better than kale, provided they have not been damaged by debris in the flood water.
  4. Risks to flooded crop plants include a range of fungal rots. These may reduce survivability of individual plants in the weeks flowing the flooding. Physical damage to bulbs or stems increases the risk of rots setting in.

4)  Flood water contaminants. Mud and silt that cover bulb crops and kale stems may increase the risk of fungal and bacterial plant diseases. Stock is less likely to eat crops covered in silt so expect feed intakes to be lower.

  • Consider contaminants that may be risky to stock and staff. Crops and supplementary feed could be contaminated with overflow from septic tanks, store of agricultural chemicals or fertiliser etc. Decisions on the risk of grazing crops or using supplementary feeds should be made on a paddock-by-paddock basis.

5) Grazing of flood affected crops. Once crops paddocks are dry enough to access, restoring power and infrastructure is top priority. Cattle must be break fed on all winter feed crops (do not set-stock or block graze).

  • Wait until conditions underfoot are suitable for grazing.
  • Ensure stock have access to good quality water while grazing winter crops.
  • Graze flood damaged crops sooner rather than later, leaving non-flooded paddocks for grazing later in winter.
  • Re-transition stock back to winter crop. Even if stock was fully transitioned before the floods. This is especially important for cattle grazing fodder beet.
  • Re-adjust break allocations in flood affected feed crops. Flooding creates greater variation in drymatter yield within each paddock. Extreme care will be needed when allocating daily breaks to account for this variation.
  • Fence off ponded areas of crop paddocks. Ducks, pukeko and other waterfowl attracted to ponded crop may spread Salmonella to stock.

6) Potential animal health risks to stock grazing flooded crop areas. These include clostridial disease (calves and hoggets in particular due to rapid changes in diet and ingestion of more mud and soil than usual), footrot and hoof damage, contaminants in flood water and copper deficiency. Excessive ingestion of mud and soil during and following flood events may result in longer-term copper deficiency.  Contact your veterinarian for animal health advice specific to your animals and situation.